Merge pull request heroku#769 from heroku/pip-pipenv-pin

Pin pip version used by pipenv

Merge pull request heroku#760 from heroku/add-airflow-110-support

Add Apache Airflow 1.10 Support

Merge pull request heroku#759 from heroku/update-travis

Update travis setup for Hatchet

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 <me@kennethreitz.org>

improve pip installation

Signed-off-by: Kenneth Reitz <me@kennethreitz.org>

fix bug with pip

Signed-off-by: Kenneth Reitz <me@kennethreitz.org>