refactor: dev optimizations

dev/webpack/webpack.prod.js

@@ -4,6 +4,7 @@ const merge = require('webpack-merge')
 const CleanWebpackPlugin = require('clean-webpack-plugin')
 const UglifyJSPlugin = require('uglifyjs-webpack-plugin')
 const ExtractTextPlugin = require('extract-text-webpack-plugin')
+const DuplicatePackageCheckerPlugin = require('duplicate-package-checker-webpack-plugin')
 
 const common = require('./webpack.common.js')
 
@@ -19,6 +20,7 @@ module.exports = merge(common, {
     new webpack.DefinePlugin({
       'process.env.NODE_ENV': JSON.stringify('production')
     }),
-    new ExtractTextPlugin('css/bundle.css')
+    new ExtractTextPlugin('css/bundle.css'),
+    new DuplicatePackageCheckerPlugin()
   ]
 })