fix(cmd): don't try to use TASKKILL on linux
fix(cmd): don't try to use TASKKILL on linux

Fixes #576

jeblair/GitPython,jeblair/GitPython,breavo/GitPython,breavo/GitPython,gitpython-developers/gitpython,gitpython-developers/GitPython,gitpython-developers/gitpython,gitpython-developers/GitPython