Fix a bug for updating diffs

Summary: Hit this issue in D8485. I think reviewedByPHID changes should appear in application transactions.

Test Plan: Would like to deploy this and try updating D8485 again.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: aran, epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8491