fix: add default listen port for server (#235)

* Add default listen port

* revise listener as requested

* Revised listener as requested

Added a space to console log

server.js

@@ -53,7 +53,8 @@ app.use(function(err, req, res, next) {
   }  
 })
 
-app.listen(process.env.PORT, function () {
-  console.log('Node.js listening ...');
+//Listen on port set in environment variable or default to 3000
+const listener = app.listen(process.env.PORT || 3000, function () {
+  console.log("Node.js listening on port " + listener.address().port);
 });