how to enable the css autoprefix function in webpack.dev.config and webpack.prod.config? I try to add the following to the vue-loader.conf.js file ``` module.exports = { loaders: utils.cssLoaders({ sourceMap: isProduction ? config.build.productionSourceMap : config.dev.cssSourceMap, extract: isProduction }), postcss: [ require('postcss-cssnext')({ browsers: ['last 20 versions'] }) ] } ``` my pakage.json file : ``` "webpack": "^2.2.1", "postcss-cssnext": "^2.10.0", "postcss-loader": "^1.3.3", ``` when I exec the npm run dev ,no autoprefix in the flex and transform css attrs thank you very much if anyone can help me