Skip copying webkitMovementX/Y

The following warnings are observed in Chrome 45.0 and 47.0 (OSX):
`'webkitMovementX' is deprecated. Please use 'movementX' instead.`

`webkitMovementX/Y` seem to be deprecated in Chrome 45+, so skip copying
them. This fix should eliminate these warnings.

src/event.js

@@ -119,7 +119,7 @@
 
   var returnTrue = function(){return true},
       returnFalse = function(){return false},
-      ignoreProperties = /^([A-Z]|returnValue$|layer[XY]$)/,
+      ignoreProperties = /^([A-Z]|returnValue$|layer[XY]$|webkitMovement[XY]$)/,
       eventMethods = {
         preventDefault: 'isDefaultPrevented',
         stopImmediatePropagation: 'isImmediatePropagationStopped',