Update all future imports for Python 2

plexpy/api2.py

@@ -18,8 +18,8 @@
 
 from __future__ import absolute_import
 from __future__ import unicode_literals
-from builtins import str
-from builtins import object
+from future.builtins import str
+from future.builtins import object
 
 import hashlib
 import inspect