fix: remove test from readme

The generated README was mentionning:

    ### Run your tests
    ```
    npm run test
    ```

but `npm run test` throws:

    Error: no test specified

This removes the mention of this command from the generated README.

packages/@vue/cli/lib/util/generateReadme.js

@@ -2,7 +2,6 @@ const descriptions = {
   build: 'Compiles and minifies for production',
   serve: 'Compiles and hot-reloads for development',
   lint: 'Lints and fixes files',
-  test: 'Run your tests',
   'test:e2e': 'Run your end-to-end tests',
   'test:unit': 'Run your unit tests'
 }