webpack.prod.js

const webpack = require('webpack');
const Merge = require('webpack-merge');
const ExtractTextPlugin = require('extract-text-webpack-plugin');
const CommonConfig = require('./webpack.common.js');

module.exports = Merge(CommonConfig, {
  module: {
    rules: [
      {
        test: /\.scss$/,
        use:  ExtractTextPlugin.extract({
          fallback: 'style-loader',
          use: ['css-loader', 'sass-loader']
        })
      } 
    ]
  },
  plugins: [
    new ExtractTextPlugin({
      filename: '[name].bundle.css',
      allChunks: true
    }),
    new webpack.optimize.UglifyJsPlugin({})
  ]
});