improve pip installation

Signed-off-by: Kenneth Reitz <[email protected]>

fix bug with pip

Signed-off-by: Kenneth Reitz <[email protected]>

pip

Signed-off-by: Kenneth Reitz <[email protected]>

upgrade pip

Signed-off-by: Kenneth Reitz <[email protected]>

don't skip Pipenv installation if there are git deps (heroku#656)

Pipenv uninstall, and other improvements (heroku#650)

Update python.gunicorn.sh (heroku#628)

Merge branch 'master' of github.com:heroku/heroku-buildpack-python

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Signed-off-by: Kenneth Reitz <[email protected]>

Merge branch 'master' of github.com:heroku/heroku-buildpack-python

changelog

Signed-off-by: Kenneth Reitz <[email protected]>