Added - to the whitelist for CSS rules

Summary: Fixes T11567. This way people can use things like sans-serif and -webkit-small-control for their "monospaced" font

Test Plan:
I added the hyphen to the regex then was able to set my Monospaced Font to be anything with a hyphen in it.

I also tried to break it pretty extensively, but couldn't find anything that would let me write malicious CSS or JS.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, yelirekim

Maniphest Tasks: T11567

Differential Revision: https://secure.phabricator.com/D16519