update bob dependency to point to internal bob-builder fork

Added this for local testing because bob requires 2.7, should not be merged to master

Pin pip version used by pipenv

Add Apache Airflow 1.10 Support

Update travis setup for Hatchet

Fix Python 3.6 message when using Python 3.7

Fix indentation levels

more helpful messages about supported versions

Hatchet/yay

Start adding dates to changelog entries

It's occasionally useful to see at a glance when releases were pushed to understand what release might have caused a customer's issues. This back-fills dates for the last few months of releases and sets a precedent that can be followed in the future.