Make grammar more consistent

Summary: In Maniphest, we say "X closed <task> by committing <commit>". In Differential, we currently say "X closed <revision> by commit <commit>", which sounds nongrammatical to me.

Test Plan: grammar'd

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11544