Updates urllib3 to 528ad3c

This includes fixes for openssl running with Pypy, so SSL connections can be
made if ndg-httpsclient, pyopenssl and pyasn1 are installed.

see also:

- https://github.com/shazow/urllib3/issues/449
- https://github.com/pypa/pip/issues/1988
Merge pull request #2179 from kevinburke/urllib3-pypy-ssl

Updates urllib3 to 528ad3c