fix scrollposition for IE

IE 11 (and below?) doesn't know scrollY, so we fallback to pageYOffset.
Didn't test if pageYOffset is the better choice for all browsers.

Author: tobaco

sloth.max.js

@@ -21,7 +21,7 @@
 					branch;
 
 				if(i){
-					wTop = context.scrollY;
+					wTop = context.scrollY || context.pageYOffset;
 					wBottom = wTop + context.innerHeight;
 
 					while(i--){
@@ -76,4 +76,4 @@
 	}else{
 		context.sloth = sloth();
 	}
-})(this);
+})(this);