Fix issue where https is not honoured when loading disqus api

Summary: Currently if disqus is used and a phame post is loaded over ssl, the disqus api is not loaded over https. This fixes that by honouring the protocol being used by the html document.

Test Plan: Open a phame post over https

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D6311