Fix suggesting Python 3.5.x on docs

[spokerman12]

Hi!

On the OCIM docs we have:

Also, remember to use Python 3.5.x or Python 3.6.x(use pyenv) for your vagrant environment as the playbooks only support them for now, and do not work on Python 3.7 or higher.

In requirements/dev.txt, requirements/base.txt and requirements/test.txt we have:

async-timeout==3.0.1

But on https://pypi.org/project/async-timeout/ (3.0.1 at the time of writing this) we see:

Requires: Python >=3.5.3

So the docs shouldn't suggest Python 3.5.x but at least Python >=3.5.3. I'd even suggest a specific version, just to save time and simplify setting up a dev environment.

I'm suggesting this because my installation failed with 3.5.2.

EDIT: Maybe I'm also at fault for not doing vagrant provision after vagrant up but then shouldn't this go on the docs too?