Update contributor_testing.rst to feature tox instead of py.test
Update contributor_testing.rst to feature tox instead of py.test

Vauxoo/cookiecutter,sp1rs/cookiecutter,lgp171188/cookiecutter,atlassian/cookiecutter,willingc/cookiecutter,lgp171188/cookiecutter,foodszhang/cookiecutter,hackebrot/cookiecutter,kkujawinski/cookiecutter,benthomasson/cookiecutter,nhomar/cookiecutter,agconti/cookiecutter,dajose/cookiecutter,audreyr/cookiecutter,takeflight/cookiecutter,drgarcia1986/cookiecutter,cguardia/cookiecutter,janusnic/cookiecutter,ramiroluz/cookiecutter,dajose/cookiecutter,pjbull/cookiecutter,drgarcia1986/cookiecutter,benthomasson/cookiecutter,stevepiercy/cookiecutter,venumech/cookiecutter,willingc/cookiecutter,nhomar/cookiecutter,hackebrot/cookiecutter,luzfcb/cookiecutter,Springerle/cookiecutter,michaeljoseph/cookiecutter,sp1rs/cookiecutter,venumech/cookiecutter,kkujawinski/cookiecutter,lucius-feng/cookiecutter,ionelmc/cookiecutter,audreyr/cookiecutter,pjbull/cookiecutter,terryjbates/cookiecutter,foodszhang/cookiecutter,atlassian/cookiecutter,Vauxoo/cookiecutter,moi65/cookiecutter,ramiroluz/cookiecutter,cguardia/cookiecutter,takeflight/cookiecutter,vintasoftware/cookiecutter,moi65/cookiecutter,janusnic/cookiecutter,lucius-feng/cookiecutter,christabor/cookiecutter,agconti/cookiecutter,christabor/cookiecutter,luzfcb/cookiecutter,stevepiercy/cookiecutter,terryjbates/cookiecutter,ionelmc/cookiecutter,vintasoftware/cookiecutter,Springerle/cookiecutter,michaeljoseph/cookiecutter