Pass author config to git with "-c x=y" instead of "--author"
Summary: See D14232. That didn't actually work. It looks like this does.
Test Plan:
- Ran git commit --author ... on build server and saw the same failure.
- Ran git -c ... -c ... commit ... on build server and saw it work.
Reviewers: chad
Reviewed By: chad
Differential Revision: https://secure.phabricator.com/D14233