use console.warn for warning

packages/babel-preset-env/src/normalize-options.js

@@ -203,7 +203,7 @@ export function normalizeCoreJSOption(
 
   if (useBuiltIns && corejs === undefined) {
     rawVersion = 2;
-    console.log(
+    console.warn(
       "\nWARNING: We noticed you're using the `useBuiltIns` option without declaring a " +
         "core-js version. Currently, we assume version 2.x when no version " +
         "is passed. Since this default version will likely change in future " +

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs-no-import/stderr.txt

@@ -0,0 +1,6 @@
+WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
+
+You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
+
+  npm install --save core-js@2    npm install --save core-js@3
+  yarn add core-js@2              yarn add core-js@3

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs-no-import/stdout.txt

@@ -1,10 +1,3 @@
-WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
-
-You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
-
-  npm install --save core-js@2    npm install --save core-js@3
-  yarn add core-js@2              yarn add core-js@3
-
 @babel/preset-env: `DEBUG` option
 
 Using targets:

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs-shippedProposals/stderr.txt

@@ -0,0 +1,6 @@
+WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
+
+You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
+
+  npm install --save core-js@2    npm install --save core-js@3
+  yarn add core-js@2              yarn add core-js@3

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs-shippedProposals/stdout.txt

@@ -1,10 +1,3 @@
-WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
-
-You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
-
-  npm install --save core-js@2    npm install --save core-js@3
-  yarn add core-js@2              yarn add core-js@3
-
 @babel/preset-env: `DEBUG` option
 
 Using targets:

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs-uglify/stderr.txt

@@ -0,0 +1,6 @@
+WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
+
+You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
+
+  npm install --save core-js@2    npm install --save core-js@3
+  yarn add core-js@2              yarn add core-js@3

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs-uglify/stdout.txt

@@ -1,11 +1,3 @@
-WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
-
-You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
-
-  npm install --save core-js@2    npm install --save core-js@3
-  yarn add core-js@2              yarn add core-js@3
-
-
 The uglify target has been deprecated. Set the top level
 option `forceAllTransforms: true` instead.
 

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs/stderr.txt

@@ -0,0 +1,6 @@
+WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
+
+You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
+
+  npm install --save core-js@2    npm install --save core-js@3
+  yarn add core-js@2              yarn add core-js@3

packages/babel-preset-env/test/debug-fixtures/entry-no-corejs/stdout.txt

@@ -1,10 +1,3 @@
-WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
-
-You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
-
-  npm install --save core-js@2    npm install --save core-js@3
-  yarn add core-js@2              yarn add core-js@3
-
 @babel/preset-env: `DEBUG` option
 
 Using targets:

packages/babel-preset-env/test/debug-fixtures/usage-no-corejs-none/stderr.txt

@@ -0,0 +1,6 @@
+WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
+
+You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
+
+  npm install --save core-js@2    npm install --save core-js@3
+  yarn add core-js@2              yarn add core-js@3

packages/babel-preset-env/test/debug-fixtures/usage-no-corejs-none/stdout.txt

@@ -1,10 +1,3 @@
-WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
-
-You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
-
-  npm install --save core-js@2    npm install --save core-js@3
-  yarn add core-js@2              yarn add core-js@3
-
 @babel/preset-env: `DEBUG` option
 
 Using targets:

packages/babel-preset-env/test/debug-fixtures/usage-no-corejs/stderr.txt

@@ -0,0 +1,6 @@
+WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
+
+You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
+
+  npm install --save core-js@2    npm install --save core-js@3
+  yarn add core-js@2              yarn add core-js@3

packages/babel-preset-env/test/debug-fixtures/usage-no-corejs/stdout.txt

@@ -1,10 +1,3 @@
-WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
-
-You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
-
-  npm install --save core-js@2    npm install --save core-js@3
-  yarn add core-js@2              yarn add core-js@3
-
 @babel/preset-env: `DEBUG` option
 
 Using targets: