updated demo to use new notation

Author: aishek

demo/index.html

@@ -24,7 +24,7 @@
       color: 'green',
       'font-size': '30px',
 
-      number_step: function(now, tween) {
+      numberStep: function(now, tween) {
         var floored_number = Math.floor(now),
             target = $(tween.elem);