Use python2

Since CouchPotato is not Python 3 compatible, this makes sure the
correct Python version is used. Even when /usr/bin/python is Python 3.

CouchPotato.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 from __future__ import print_function
 from logging import handlers
 from os.path import dirname