Fix arc browse path:line
Summary: Ref T5781. This was broken in some earlier changes in T5781.
Test Plan: Ran arc browse README, arc browse README:10.
Reviewers: chad, btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T5781
Differential Revision: https://secure.phabricator.com/D10346