replace Constrainable with ConstrainablePattern per https://www.w3.org/Bugs/Public/show_bug.cgi?id=25604
couple of typos
Merge branch 'bug25604' of https://github.com/dontcallmedom/webrtc-w3c into dontcallmedom-bug25604
Merge branch 'dontcallmedom-bug25604'