fix coveralls on python 3.3

[tomato42]

The execution of coveralls on 3.3 fails, which means the coverage data is not uploaded:

$ if [[ -z $INSTRUMENTAL ]]; then coveralls; fi
Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.3.6/bin/coveralls", line 11, in <module>
    sys.exit(wear())
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/coveralls/__init__.py", line 95, in wear
    skip_ssl_verify=args.skip_ssl_verify,
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/coveralls/api.py", line 8, in post
    return requests.post(url, files={'json_file': json_file}, verify=(not skip_ssl_verify))
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/requests/api.py", line 119, in post
    return request('post', url, data=data, json=json, **kwargs)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/requests/api.py", line 61, in request
    return session.request(method=method, url=url, **kwargs)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/requests/sessions.py", line 530, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/requests/sessions.py", line 643, in send
    r = adapter.send(request, **kwargs)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/requests/adapters.py", line 449, in send
    timeout=timeout
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/urllib3/connectionpool.py", line 677, in urlopen
    chunked=chunked,
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/urllib3/connectionpool.py", line 381, in _make_request
    self._validate_conn(conn)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/urllib3/connectionpool.py", line 978, in _validate_conn
    conn.connect()
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/urllib3/connection.py", line 371, in connect
    ssl_context=context,
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/urllib3/util/ssl_.py", line 350, in ssl_wrap_socket
    context.load_verify_locations(ca_certs, ca_cert_dir, ca_cert_data)
TypeError: load_verify_locations() takes at most 2 arguments (3 given)
Done. Your build exited with 0.

find version of coveralls that works on 3.3, or if not possible, disable it there completely