adding miniCSSExtractPlugin to webpack code example

Example: mini-css-extract-plugin sass

//installation
npm install --save-dev mini-css-extract-plugin

//configuration
const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
  plugins: [new MiniCssExtractPlugin()],
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [MiniCssExtractPlugin.loader, 'css-loader'],
      },
    ],
  },
};