Wouldn't be necessary if pip would do proper version management.
As things are right now, pip ignores the urllib3 version requirements
from requests because gallery-dl is specifying its own.
urllib3 versions 1.24.1 and 1.24.2 cause HTTP requests to
https://www.artstation.com/users/<username>/quick.json
to fail with a 403: Forbidden status code (#227),
and provoke a CAPTCHA response after solving a Cloudflare challenge.
- uses an OrderedDict for session.headers (since 2.9.2)
- ships with urllib3 1.16, which is the first version to have an
'allowed_gai_family()' function
