Merge pull request heroku#736 from heroku/v-138

v 138 changelog

Prevent 3.7.0 from appearing as unsupported in buildpack messaging.

Merge pull request heroku#722 from heroku/python-3.7-and-3.6.6

Build Python 3.6.6 and 3.7.0

Release version 135 with new Pipenv version lock

buildpack.toml

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

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)