Change shebang to /usr/bin/env python

Using /usr/bin/python might have side-effects, such as the system
python being used even when the script is called from within a
python virtual env. env python should give us the right interpreter.
As we are both python2 and python3 compatible this should cause no
problems.

servefile

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
 # Licensed under GNU General Public License v3 or later