fix: add port fallback (#23)

Add fallback to port 3000, if PORT in env is not defined

server.js

@@ -28,6 +28,6 @@ app.get("/api/hello", function (req, res) {
 
 
 // listen for requests :)
-var listener = app.listen(process.env.PORT, function () {
+var listener = app.listen(process.env.PORT || 3000, function () {
   console.log('Your app is listening on port ' + listener.address().port);
 });