Add scope hoisting in the prod config (#1013)

https://medium.com/webpack/brief-introduction-to-scope-hoisting-in-webpack-8435084c171f

Author: agnivade

template/build/webpack.prod.conf.js

@@ -73,6 +73,8 @@ const webpackConfig = merge(baseWebpackConfig, {
     }),
     // keep module.id stable when vender modules does not change
     new webpack.HashedModuleIdsPlugin(),
+    // enable scope hoisting
+    new webpack.optimize.ModuleConcatenationPlugin(),
     // split vendor js into its own file
     new webpack.optimize.CommonsChunkPlugin({
       name: 'vendor',