Upgrade requests version

[davidfischer]

This is related to a production issue with the older requests version.

[humitos]

Be careful with requests upgrade since it's not fully compatible with all versions of docker-py: #3243 (comment)

[davidfischer]

If anything, we want to upgrade further. docker/docker-py@3b95da3

[humitos]

I agree. I'd like to upgrade docker and requests to the latest version available. We need to consider that RTD servers will be using 17.05.0~ce-0~ubuntu-xenial which is also not the latest docker engine. So, we need to be carefull that these three dependencies work all together :)

Ref: https://github.com/readthedocs/readthedocs-ops/pull/233

[ericholscher]

Do we know if these are safe? Did we hotfix prod for the issue the other day with this version? @agjohnson

[agjohnson]

I used 2.9.1 (system version) as the first version that wasn't reproducing the error. I don't see a reason to not go higher though. I didn't test this at all though

[agjohnson]

This is needed. Higher bump can be done later.