Allow Feed HTTP hooks to be https://

Summary: Fixes T3503. "HTTPFuture" is specialized and HTTP-only; "HTTPSFuture" is generalized and HTTP+HTTPS.

Test Plan: yeah not so much

Reviewers: btrahan, edward

Reviewed By: edward

CC: aran

Maniphest Tasks: T3503

Differential Revision: https://secure.phabricator.com/D6378