[Bug] ESLint Loader is deprecated: ESLint Webpack Plugin should be the alternative

[tropicalraisel]

I've changed out .enableEslintLoader({ ... }) to the following:

.addPlugin(new ESLintPlugin({
      files: 'assets/javascripts/',
      fix: true,
      threads: true
    }))

but just a heads-up that it should be switched out, and probably renamed to .enableEslintPlugin.

[tropicalraisel]

Addressed by Pull Request #985