urllib3 update

#1053
Merge pull request #1180 from sigmavirus24/master

Fix Session level Cookie Handling
Fix of UnicodeDecodeError on unicode header name that can be converted to ascii.
removed no longer used redirect codes from models
added numeric values of redirect codes in comments
Deleted is_py2 check from unicode_header_name fix thanks to Lukasa.
Merge pull request #1184 from piotr-dobrogost/numeric_codes

small cleanup of redirect codes
Merge pull request #1181 from denis-ryzhkov/master

Fix of UnicodeDecodeError on unicode header name that can be converted to ascii.