removed undeclared var

app.js

@@ -8,7 +8,7 @@ var bpm = 120;
 var stepPos = 0;
 
 http.listen(port, function() {
-    console.log('Listening on port %d', server_port);
+    console.log('Listening on port: '+port);
 });
 
 app.use(express.static(__dirname + '/public'));