fix: eslint package path for cache (#283)

index.js

@@ -160,21 +160,35 @@ module.exports = function(input, map) {
     loaderUtils.getOptions(webpack)
   );
 
-  var userEslintPath = userOptions.eslintPath;
-
   var eslintPkgPath = "eslint/package.json";
-  if (userEslintPath) {
-    eslintPkgPath = userEslintPath + "/package.json";
+  var userEslintPath = eslintPkgPath;
+
+  if (userOptions.eslintPath) {
+    userEslintPath = userOptions.eslintPath + "/package.json";
+  }
+
+  var eslintVersion;
+
+  try {
+    eslintVersion = require(require.resolve(userEslintPath)).version;
+  } catch (_) {
+    // ignored
   }
 
-  var eslintVersion = require(eslintPkgPath).version;
+  if (!eslintVersion) {
+    try {
+      eslintVersion = require(require.resolve(eslintPkgPath)).version;
+    } catch (_) {
+      // ignored
+    }
+  }
 
   var config = assign(
     // loader defaults
     {
       cacheIdentifier: JSON.stringify({
         "eslint-loader": pkg.version,
-        eslint: eslintVersion
+        eslint: eslintVersion || "unknown version"
       }),
       eslintPath: "eslint"
     },