Fixed Issue #550

Changed the update function to check for the originalEvent.type
rather than the event.type to be more compatible with other libraries
that could rewrite the default resize event.

Demos:
Before fix:
http://demos.heydanwaz.com/fancybox/no-isotope.html - event and originalEvent are the same
http://demos.heydanwaz.com/fancybox/with-isotope.html - event and originalEvent are different

After:
http://demos.heydanwaz.com/fancybox/with-isotope-fix.html