Fix python version detection in theme bobthefish
Fix python version detection in theme bobthefish

Relax the python version matching, so `python` that symlinks to
either major versions (e.g. 2, 3) or minor versions (e.g. 2.7, 3.4)
can be properly detected.

Note that currently both pypy and pypy3 have same display glyph.

oh-my-fish/theme-bobthefish