Enable sourceMap in production environment (#32)

https://webpack.js.org/how-to/upgrade-from-webpack-1/#uglifyjsplugin-sourcemap

Enable sourceMap in production environment

template/webpack.config.js

@@ -53,6 +53,7 @@ if (process.env.NODE_ENV === 'production') {
       }
     }),
     new webpack.optimize.UglifyJsPlugin({
+      sourceMap: true,
       compress: {
         warnings: false
       }