[effects/scale] Don't animate popups on Wayland

I made a horrible typo("popup" vs "popupWindow"), which went
unnoticeable during code review and while I was testing the ported
effect on Wayland.

Because this change is pretty trivial (fixing a typo), I didn't put it
on review.

effects/scale/package/contents/code/main.js

@@ -62,7 +62,7 @@ var scaleEffect = {
         }
 
         // Don't animate combobox popups, tooltips, popup menus, etc.
-        if (window.popup) {
+        if (window.popupWindow) {
             return false;
         }