py-six: update to 1.11.0

1.11.0:

- Pull request 178: `with_metaclass` now properly proxies `__prepare__` to the
  underlying metaclass.

- Pull request 191: Allow `with_metaclass` to work with metaclasses implemented
  in C.

- Pull request 203: Add parse_http_list and parse_keqv_list to moved
  urllib.request.

- Pull request 172 and issue 171: Add unquote_to_bytes to moved urllib.parse.

- Pull request 167: Add `six.moves.getoutput`.

- Pull request 80: Add `six.moves.urllib_parse.splitvalue`.

- Pull request 75: Add `six.moves.email_mime_image`.

- Pull request 72: Avoid creating reference cycles through tracebacks in
  `reraise`.

(adam)