Specify the buildpack_url so we use the node.js buildpack

Author: Edward Muller

app.json

@@ -4,6 +4,9 @@
   "keywords": [ "react", "reactjs", "tutorial" ],
   "repository": "https://github.com/reactjs/react-tutorial",
   "website": "http://facebook.github.io/react/docs/tutorial.html",
-  "success_url": "/"
+  "success_url": "/",
+  "env" : {
+    "BUILDPACK_URL": "https://github.com/heroku/heroku-buildpack-nodejs.git"
+  }
 }