R1:4b15871ced9e

Fix specification of `ttl.relative` via LFS

Summary: Fixes T12828. This API was tightened up D17616, but I missed this callsite.

Test Plan: I've just got a good feeling in my bones.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12828

Differential Revision: https://secure.phabricator.com/D18119