添加es3ify-loader 无效

var webpack = require('webpack')
var es3ifyPlugin = require('es3ify-webpack-plugin');

module.exports = {
entry: {

'main': path.resolve('src', 'entry.js')

},
output: {

filename: '[name].js',
path: path.resolve(__dirname, 'dist')

},
module: {

loaders: [{
  test: /\.js$/,
  exclude: /node_modules/,
  loaders: ['babel-loader'],
}, ],
postLoaders: [{
  enforce: "post",
  test: /\.js$/,
  loaders: ['es3ify-loader'],
}],

},
plugins: [

 new es3ifyPlugin(),
 new webpack.optimize.UglifyJsPlugin({
   mangle: false,
   compress: {
     warnings: false,
     screw_ie8: false
   },
   output: {
     // comments: false,
     screw_ie8: false
   }
 }),

]
}