fix ping message

assets/js/sumorobot.js

@@ -41,7 +41,7 @@ Sumorobot.prototype.connect = function() {
         // Setup a timer to ping the robot
         self.watchdogTimer = setInterval(function() {
             // Send a ping to the robot
-            self.send(self.robotId, 'ping');
+            self.send('ping');
         }, 500);
     };
     // When the WebSocket closes