change NODE_ENV to follow recommendations from webpack (#1622)

* change NODE_ENV to follow recommendations from weback

* Update deployment.md

Author: parkourben99

src/v2/guide/deployment.md

@@ -36,9 +36,7 @@ module.exports = {
   plugins: [
     // ...
     new webpack.DefinePlugin({
-      'process.env': {
-        NODE_ENV: JSON.stringify('production')
-      }
+      'process.env.NODE_ENV': JSON.stringify('production')
     })
   ]
 }