Shebangs with spaces are not corrected by our sed

See:

https://src.fedoraproject.org/rpms/chromium/pull-request/11

chromium used a copy pasted sed from our guide. yet it was wrong.

The problematic shebang was (something like):

#! /usr/bin/env python

Notice the space.

BTW Instead of fixing the shebang in the guide and making it even more complicated, we can recommend pathfix.py as described in https://github.com/fedora-python/python-rpm-porting/issues/24