Declare that revision was closed by committer, not author

Summary: D2703#13 is confusing - it looks like that @allenjohnashton took the action but it was @epriestley.

Test Plan: I don't have a repro so I tested this block standalone.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2707