Adding fallback to port 4200 for development server

nodeapp/app.js

@@ -117,6 +117,6 @@ app.get('/cleanup', (req, res) => {
 
 
 // listen for requests :)
-const listener = app.listen(process.env.PORT, function() {
+const listener = app.listen(process.env.PORT || 4200, function() {
   console.log("Your app is listening on port " + listener.address().port);
 });