Downgrade mock to 3.0.5 for Python 2.7 compatibility

* Only required for plexapi tests

lib/mock/__init__.py

@@ -1,15 +1,4 @@
 from __future__ import absolute_import
-
-import re, sys
-
-IS_PYPY = 'PyPy' in sys.version
-
 import mock.mock as _mock
 from mock.mock import *
-
-__version__ = '4.0.2'
-version_info = tuple(int(p) for p in
-                     re.match(r'(\d+).(\d+).(\d+)', __version__).groups())
-
-
-__all__ = ('__version__', 'version_info') + _mock.__all__
+__all__ = _mock.__all__