Add python-phabricator as a directory we need to update.

Test Plan:
Will run ./update_phabricator.sh and make sure it updates this fake-subrepo.
Sanity check.

I don't know when I wrote this, but it's been in my repo for forever
I'm guessing?  Or something.

Auditors: chris

Test Plan:
Fingers crossed.
merge from upstream phabricator