R1:508f1b19f966

[easy] Add limit param to recent commits

Summary: as title

Test Plan: https://phabricator.fb.com/conduit/method/diffusion.getrecentcommitsbypath/

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2838