Replace "env python" by "env python2/3"

[dertuxmalwieder]

While the Python binaries are in most cases available as "python2" or "python3", OSX and BSD systems (and probably some Linuxes too) don't link "python2" or "python3" to "python" automatically. You might consider to consider that.

Another advantage of that would be that you could stop supporting the deprecated Python2 line. :-)