fix(test_cmd): handle GitCommandNotFound in test
fix(test_cmd): handle GitCommandNotFound in test

Related to #248

StyXman/GitPython,expobrain/GitPython,StyXman/GitPython,pengshp/GitPython,h4ck3rm1k3/GitPython,roidelapluie/GitPython,beni55/GitPython,ghtdak/GitPython,avinassh/GitPython,gitpython-developers/gitpython,cdht/GitPython,breavo/GitPython,avinassh/GitPython,gitpython-developers/gitpython,cdht/GitPython,cdht/GitPython,StyXman/GitPython,expobrain/GitPython,roidelapluie/GitPython,zsjohny/GitPython,zsjohny/GitPython,beni55/GitPython,dpursehouse/GitPython,nvie/GitPython,pengshp/GitPython,dpursehouse/GitPython,pengshp/GitPython,h4ck3rm1k3/GitPython,ghtdak/GitPython,bwrsandman/GitPython,bwrsandman/GitPython,breavo/GitPython,manasdk/GitPython,bwrsandman/GitPython,gitpython-developers/GitPython,jeblair/GitPython,avinassh/GitPython,nvie/GitPython,jeblair/GitPython,manasdk/GitPython,gitpython-developers/GitPython,zsjohny/GitPython