Eliminate Opera vendor prefix

Since [Opera is moving to Webkit](http://my.opera.com/ODIN/blog/300-million-users-and-move-to-webkit) I was wondering if it would be OK to not require `-o` prefixed vendor properties in the “[Require compatible vendor prefixes](https://github.com/stubbornella/csslint/blob/master/src/rules/compatible-vendor-prefixes.js)” rule?