Use pipenv install instead of pip inside Dockerfile

[mabdullahabid]

As the subject states, what are your thoughts on using pipenv install inside the Dockerfile instead of pip?

[wsvincent]

Dockerfile works well loading a requirements.txt file. I had lots of issues with a lockfile that might be generated locally vs within Docker, but that is probably easy enough to fix. Pipenv only just added a native way to generate requirements.txt so it's probably fine, I'm just used to using Pip and haven't had issues with that approach.