Also added Pipfile(.lock) prior to the remaining source, improving Docker image cacheability.
Git is also required to fetch pyyaml.
This results in more deterministic and reproducible image builds, since httpbin dependencies
are installed using locked versions from Pipfile.lock before httpbin is itself installed.
Fixed#493.
As @kennethreitz likes to say:
> The use of Python 3 is highly preferred over Python 2. Consider upgrading
> your applications and infrastructure if you find yourself still using Python
> 2 in production today. If you are using Python 3, congratulations — you are
> indeed a person of excellent taste.
Brett Randall
kennethreitz