Add RSS of Bugzilla query of open HHVM bugs to mediawikiwiki's whitelist

To be transcluded in [[mw:HHVM]].

Change-Id: Id6222f4db8bf24c92e52ca093d67c4396d21f8a8
Merge "Add RSS of Bugzilla query of open HHVM bugs to mediawikiwiki's whitelist"