Fixed localcommits include on getDiffDict

Summary: Ref T10808

Test Plan: Call differential.querydiffs method and expect 'local:commits' property be added to the result.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Maniphest Tasks: T10808

Differential Revision: https://secure.phabricator.com/D15710