Update debug build warning message

src/scaffolding/export.js

@@ -5,7 +5,7 @@ if (window.Scaffolding) {
 }
 
 if (process.env.NODE_ENV !== 'production') {
-  console.log('Not a production build. Set NODE_ENV to production or use `npm run build-prod` for improved file size and performance (This message will go away).');
+  console.log('This is not a production build. Set NODE_ENV to production or use `npm run build-prod` for improved file size and performance (This message will go away).');
 }
 
 window.Scaffolding = Scaffolding;