Build React in production mode by default

https://facebook.github.io/react/downloads.html says:
"By default, React will be in development mode. To use React in production mode, set the environment variable NODE_ENV to production (using envify or webpack's DefinePlugin). A minifier that performs dead-code elimination such as UglifyJS is recommended to completely remove the extra code present in development mode."

webpack.config.js

@@ -148,6 +148,12 @@ const config = [
         jQuery: 'jQuery',
         $: 'jQuery',
       }),
+      new webpack.DefinePlugin({
+        'process.env':{
+          // Builds React in production mode, avoiding console warnings
+          'NODE_ENV': JSON.stringify('production')
+        }
+      }),
       new webpack.optimize.UglifyJsPlugin({
         compress: {
           unused: false,