update get-pip to look for sha
update get-pip to look for sha

skilljar/heroku-buildpack-python,benmurden/heroku-buildpack-python-ember,heroku/heroku-buildpack-python,Scalingo/python-buildpack,heroku/heroku-buildpack-python,Scalingo/python-buildpack,benmurden/heroku-buildpack-python-ember,AltSchool/heroku-buildpack-python,AltSchool/heroku-buildpack-python