Release 3.2 broke python2 support

According to the NEWS file and setup.py, mailmanclient 3.2 is still supposed to support python2.7. But apparently it does not:

# python
Python 2.7.15 (default, Jul 28 2018, 11:29:29) 
[GCC 8.1.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import mailmanclient
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/mailmanclient/__init__.py", line 25, in <module>
    from mailmanclient.client import Client
  File "/usr/lib/python2.7/dist-packages/mailmanclient/client.py", line 36, in <module>
    from mailmanclient.restbase.connection import Connection
  File "/usr/lib/python2.7/dist-packages/mailmanclient/restbase/connection.py", line 18, in <module>
    from urllib.error import HTTPError
ImportError: No module named error
>>> import urllib
>>> from urllib.error import HTTPError
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named error