title: css autoprefixer with webpack
body: <p>I have been trying to configure webpack with LESS and Autoprefixer, but autoprefixer does not seem to work. My css or less files are not autoprefixed. Example:
  <code>display: flex</code> stays <code>display: flex</code></p>
  
  <p>I have put my webpack config below:</p>
  
  <pre><code>var autoprefixer = require('autoprefixer');
  
  module.exports = {
    entry: {
      bundle: "./index.jsx"
    },
    output: {
      path: __dirname,
      filename: "[name].js"
    },
    module: {
      loaders: [
        {
          test: /\.jsx$/,
          exclude: /(node_modules|bower_components)/,
          loaders: ['react-hot', 'babel-loader']
        },
        {
          test: /\.less$/,
          loader: ExtractTextPlugin.extract("style-loader", "css-loader!postcss-loader!less-loader")
        },
        {
          test: /\.css$/,
          loader: ExtractTextPlugin.extract("style-loader", "css-loader!postcss-loader")
        }
  
      ],
      postcss: function () {
        return [autoprefixer];
      }
    },
    plugins: [
      new webpack.BannerPlugin(banner),
      new ExtractTextPlugin("style.css")
    ],
    devtool: 'source-map',
    devServer: {
      stats: 'warnings-only',
    }
  };
  </code></pre>