Fix herald "Repository" rule for Revisions and Diffs

Summary: This was broken by rP5ac36e8 by a derpy typo.

Test Plan: Ran dry run against a revision with a a repository, saw the field fill in on the transcript.

Reviewers: nickz, btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10326