Update python env for HA dev

Hi there,

I installed HA dev based on Dockerfile.dev
Everything is running smoothly and I pull the repo on a regular basis.
The ha config and ha repo are volumes on my host machine, shared with the container.

Now I see requirements_* are updated which means even though HA source code is up to date, my python env is not.

The question is : how do I update python correctly to match the requirements ? (tox is also installed)
So I can commit my docker container and have a new image after updating.
I have no experience with python. I think HA is a great way to learn.

Thank you very much.