Use python2 instead of python in arc anoid shebang`

Summary:
With the old shebang of #!/usr/bin/env python on machines with python 3 as the default python it would fail.
Prefer an explicit python2 like PEP 394 suggests.

Test Plan: ran ./arc anoid and played a game

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D15408