Change hash-bang for maximum compatability

This is to fix https://github.com/kivy/python-for-android/issues/88
The ideal solution, according to Python PEP 0394, would seem to be 
'#!/usr/bin/env python2', however that PEP is unfortunately not 
well-followed by OSX and even Linux distros like Arch and Debian 
Squeeze. Because of this, and because Kivy currently only supports 
Python2.7, the more practical solution is '#!/usr/bin/env python2.7'.