webpack3版本对应extract-text-webpack-plugin

webpack4+mini-css-extract-plugin

webpack4 需要使用mini-css-extract-plugin 2以下的版本，具体版本可在 https://www.npmjs.com/package/mini-css-extract-plugin 查看

//  webpack3 下extract-text-webpack-plugin@3.0.2
const ExtractTextPlugin = require("extract-text-webpack-plugin")
return ExtractTextPlugin.extract({
        use: loaderArray,
        fallback: "vue-style-loader"
      });
// webpack4 下mini-css-extract-plugin@1.6.2
const ExtractTextPlugin = require("mini-css-extract-plugin")
return [ExtractTextPlugin.loader].concat(loaderArray)