Update link to closure-library issue

src/ol/map.js

@@ -601,7 +601,7 @@ ol.Map.prototype.getEventPixel = function(event) {
   // but touchend and touchcancel events have no targetTouches when
   // the last finger is removed from the screen.
   // So we ourselves compute the position of touch events.
-  // See https://code.google.com/p/closure-library/issues/detail?id=588
+  // See https://github.com/google/closure-library/pull/323
   if (goog.isDef(event.changedTouches)) {
     var touch = event.changedTouches.item(0);
     var viewportPosition = goog.style.getClientPosition(this.viewport_);