Add production node env to test react build

Author: erwstout

dist/ReactCardFlipper.js

@@ -27,7 +27,12 @@ module.exports = env => {
       ]
     },
     plugins: [
-      env.production ? new webpack.optimize.UglifyJsPlugin() : ''
+      env.production ? new webpack.optimize.UglifyJsPlugin() : '',
+      new webpack.DefinePlugin({
+      "process.env": {
+         NODE_ENV: JSON.stringify("production")
+       }
+    }),
     ]
   }
 };