title: Importing Moment.js makes webpack build fail
body: <p>been getting this weird error when trying to run <code>npm run prod</code> within my Laravel project.</p>
  <blockquote>
  <p>92% chunk asset optimization OptimizeCssAssetsWebpackPluginCssSyntaxError: /css/app.css:3032:19: Missed semicolon</p>
  </blockquote>
  <p>It appears to work fine if I remove this following import within on of my components:</p>
  <pre class="lang-js prettyprint-override"><code>import moment from 'moment';
  export default {
      filters: {
          humanTimestamp: function(timestamp) {
              return moment.unix(timestamp).fromNow();
          }
      },
  </code></pre>
  <p>This is my <code>webpack.mix.js</code></p>
  <pre class="lang-js prettyprint-override"><code>let mix = require('laravel-mix');
  
  /*
   |--------------------------------------------------------------------------
   | Mix Asset Management
   |--------------------------------------------------------------------------
   |
   | Mix provides a clean, fluent API for defining some Webpack build steps
   | for your Laravel application. By default, we are compiling the Sass
   | file for the application as well as bundling up all the JS files.
   |
   */
  
  mix.js('resources/assets/js/app.js', 'public/js')
     .less('resources/assets/less/app.less', 'public/css')
     .less('resources/assets/less/documentation.less', 'public/css').version();
  
  mix.webpackConfig({
      output: {
          filename: '[name].js',
          chunkFilename: 'js/chunks/[contenthash].js',
      },
      resolve: {
          alias: {
              '@': __dirname + '/resources/assets/js/'
          }
      },
  });
  </code></pre>
  <p>And this is my <code>webpack.config.js</code></p>
  <pre class="lang-js prettyprint-override"><code>const VuetifyLoaderPlugin = require('vuetify-loader/lib/plugin');
  
  module.exports = {
      plugins: [
          new VuetifyLoaderPlugin()
      ],
      rules: [
          {
              test: /\.s(c|a)ss$/,
              use: [
                  'vue-style-loader',
                  'css-loader',
                  {
                      loader: 'sass-loader',
                      options: {
                          implementation: require('sass'),
                          sassOptions: {
                              fiber: require('fibers'),
                              indentedSyntax: true // optional
                          },
                      },
                  },
              ],
          },
      ],
  }
  </code></pre>