Allow tools51.n.o php-fpm to read Git repository

Summary:
Nowadays, Git refuses by default to read a .git directory owned
by any third-party user, if not explicitly whitelisted.

Test Plan:
Browse https://tools51.nasqueron.org and check if the Git revision
is printed in the footer.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3557