update requirements for doc creation

[ixje]

What current issue(s) does this address, or what feature is it adding?
the requirements for just creating documentation were heavily outdated.

How did you solve this problem?
created a fresh install/venv, make doc'ed + pip install until all missing packages were resolved.

How did you make sure your solution works?
make doc
Are there any special changes in the code that we should be aware of?
no
Please check the following, if applicable:

• Did you add any tests?
• Did you run make lint?
• Did you run make test?
• Are you making a PR to a feature branch or development rather than master?
• Did you add an entry to CHANGELOG.rst? (if not, please do)

[localhuman]

Last time I checked, the Read the Docs server that builds the docs can only be done with Python 3.5, so I know upgrading neo-boa ( which won't work with 3.5 ) will break the docs server build.

[ixje]

Oh didn't know that. I only tested locally. Any way to test without pushing here?
I think there's a good chance python 3.6 is now supported, see:

• Pointed users to Python3.6 readthedocs/readthedocs.org#3817
• Update install.rst dropped the Python 2.7 only part readthedocs/readthedocs.org#3814 (comment)

[localhuman]

That would be great if they're supporting 3.6 venv now! I can switch the build to the development branch to see if it works after merging this-

[ixje]

I'll leave it up to you to take further then 👍