AntennaTracker: fix for scheduler API change

AntennaTracker/AntennaTracker.pde

@@ -254,7 +254,7 @@ void setup()
     init_tracker();
 
     // initialise the main loop scheduler
-    scheduler.init(&scheduler_tasks[0], sizeof(scheduler_tasks)/sizeof(scheduler_tasks[0]), NULL);
+    scheduler.init(&scheduler_tasks[0], sizeof(scheduler_tasks)/sizeof(scheduler_tasks[0]));
 }
 
 /**