Allow urllib 1.23 (part 2)

[yan12125]

Follow-up of #4669

This eliminates the following warning:

$ python -c 'import requests'
/usr/lib/python3.6/site-packages/requests/__init__.py:80: RequestsDependencyWarning: urllib3 (1.23) or chardet (3.0.4) doesn't match a supported version!
  RequestsDependencyWarning)

[nateprewitt]

Hmm, thanks @yan12125. This is why we usually do all of these steps at once. I may have jumped the gun this morning by merging th first PR. Rather than merge multiple follow ups, I think we’ll wait until we’re ready to release, likely next week to get everything wrapped up. I’ll try to go through this tonight and get things tidied with the urllib3 upgrade.

[yan12125]

No problem and thanks for the awesome work! Indeed most likely there will be more follow-ups - I just tried to run tests locally and some of them failed with urllib3 1.23. Not sure why Travis CI and AppVeyor didn't catch them, though.

[maxnbk]

when would this get released to pypi?

[yan12125]

@maxnbk: According to this comment: #4673 (comment) - a week or so