Fixed event name typo touchcancle to touchcancel

Updated the file and fixing the typo  on `touchcancel` event.

examples/whiteboard/public/main.js

@@ -20,7 +20,7 @@
   //Touch support for mobile devices
   canvas.addEventListener('touchstart', onMouseDown, false);
   canvas.addEventListener('touchend', onMouseUp, false);
-  canvas.addEventListener('touchcancle', onMouseUp, false);
+  canvas.addEventListener('touchcancel', onMouseUp, false);
   canvas.addEventListener('touchmove', throttle(onMouseMove, 10), false);
 
   for (var i = 0; i < colors.length; i++){