Rebuild Lato fonts for Firefox

Summary: Rebuilt Lato font for Firefox, x-height to 100%. Ref T8755

Test Plan: Test Firefox without having a local copy of Lato installed on my Mac.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8755

Differential Revision: https://secure.phabricator.com/D13556