Removed visibility: hidden !important from .hidden class

This .hidden was taken from HTML 5 Boilerplate and yesterday we discussed on twitter that visibility: hidden !important can be removed now. https://twitter.com/jitendravyas/status/562940090553733121

less/utilities.less

@@ -44,7 +44,6 @@
 
 .hidden {
   display: none !important;
-  visibility: hidden !important;
 }