title: Receiving CssSyntaxError when I updated Webpack 3 to 4
body: <p>I got CssSyntaxError when I updated webpack 3 to 4.I use vue and webpack in frontside.The error is like this.</p>
  
  <pre><code>    [./node_modules/css-loader/dist/runtime/api.js] 2.35 KiB {mini-css-extract-plugin} [built]
  
      ERROR in ./app/javascript/hoge.scss (./node_modules/css-loader/dist/cjs.js??ref--3-2!./app/javascript/hoge.scss)
      Module build failed (from ./node_modules/css-loader/dist/cjs.js):
      CssSyntaxError
  
      (891:6) Unknown word
  
        889 |   background-color: #eeeeee;
        890 |   box-shadow: 0px 0px 5px #000;
      &gt; 891 |   // line-height: 0;
            |      ^
        892 | }
  </code></pre>
  
  <p>To update webpack I try to use MiniCssExtractPlugin.
  updated npm version is like below.</p>
  
  <pre><code>webpack                   latest  3.12.0  ❯  4.30.0
  webpack-dev-server        latest  2.11.1  ❯  3.3.1 
  vue                       latest  2.5.21  ❯  2.6.10
  vue-loader                latest  14.2.3  ❯  15.7.0  
  css-loader                latest  1.0.1   ❯  2.1.1 
  sass-loader@7.1.0
  </code></pre>
  
  <p>My webpack.config.js is like this below.</p>
  
  <pre><code>const MiniCssExtractPlugin = require('mini-css-extract-plugin')
  
  
  
  
  
    plugins: [
      new MiniCssExtractPlugin({
        filename: '[name]-[hash].css'
      }),
      new VueLoaderPlugin()
    ],
    module: {
      rules: [
        {
          test: /\.(scss|sass)$/,
          use: [
            'vue-style-loader',
            {
              loader: MiniCssExtractPlugin.loader
            },
            {
              loader: 'css-loader',
              options: { modules: true }
            },
            {
              loader: 'sass-loader'
            }
          ]
        },
        {
          test: /\.(css)$/,
          use: [
            'vue-style-loader',
            {
              loader: MiniCssExtractPlugin.loader
            },
            {
              loader: 'css-loader',
              options: { modules: true }
            }
          ]
        }
      ]
    }
  
  </code></pre>
  
  <p>Is there any wrong setting in webpack.config.js?</p>