Plugin list without extension not working anymore

[jclaessens97]

In relation to this issue and comment, just adding e.g. 'utc' in the list of plugins doesn't work (anymore?) when building for production:

export default {
  locales: ['en'],
  defaultLocale: 'en',
  plugins: ['utc'],
};

This does seem to work:

export default {
  locales: ['en.js'],
  defaultLocale: 'en',
  plugins: ['utc.js'],
};

Edit: same for locales apparently