使用webpack压缩css问题

Question

麻烦看看这段代码，打包的css可以分离出来但是没有压缩，已经设置minimize: true

const webpack = require('webpack');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const ExtractTextPlugin = require('extract-text-webpack-plugin');
const CleanWebpackPlugin = require('clean-webpack-plugin');
let pathsToClean = [
    'build'
  ]
module.exports = {
    entry: __dirname + "/app/main.js",//已多次提及的唯一入口文件
    output: {
        path: __dirname + "/build",
        filename: "bundle.js"
    },
    devtool: false,
    devServer: {
        contentBase: "./public",//本地服务器所加载的页面所在的目录
        historyApiFallback: true,//不跳转
        inline: true//实时刷新
    },
    module: {
        rules: [
            {
                test: /(\.jsx|\.js)$/,
                use: {
                    loader: "babel-loader"
                },
                exclude: /node_modules/
            },
            {
                test: /\.(less|css)$/,
                use: ExtractTextPlugin.extract({
                  fallback: 'style-loader',
                  //resolve-url-loader may be chained before sass-loader if necessary
                  use: [{
                    loader: "css-loader",
                    options: {
                      minimize: true //压缩css
                    }
                  }, {
                    loader: "postcss-loader"
                  },{
                    loader:"less-loader"
                  }]
                })
                
            }
        ]
    },
    plugins: [
        new webpack.BannerPlugin('版权所有，翻版必究'),
        new HtmlWebpackPlugin({
            template: __dirname + "/app/index.html"//new 一个这个插件的实例，并传入相关的参数
        }),
        new CleanWebpackPlugin(pathsToClean),
        new ExtractTextPlugin("css/style_[chunkhash].css"),
        new webpack.optimize.UglifyJsPlugin({ //压缩js文件
          compress: {   //压缩代码
            dead_code: true,  //移除没被引用的代码
            warnings: false,   //当删除没有用处的代码时，显示警告
            loops: true //当do、while 、 for循环的判断条件可以确定是，对其进行优化
          },
          except: ['$super', '$', 'exports', 'require']  //混淆,并排除关键字
        })
    ],
};