Minor linter fixes

Summary: Apply some linter autofixes.

Test Plan: `arc lint` and `arc unit`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10568
Merge branch 'master' of github.com:facebook/arcanist