Reenable UglifyJS source maps

Author: mxstbr

config/webpack.config.prod.js

@@ -120,6 +120,7 @@ module.exports = {
     new webpack.optimize.OccurrenceOrderPlugin(),
     new webpack.optimize.DedupePlugin(),
     new webpack.optimize.UglifyJsPlugin({
+      sourceMap: true,
       compressor: {
         screw_ie8: true,
         warnings: false