Fix lint issues caught by new pylint (#166)

google/auth/transport/urllib3.py

diff --git a/google/auth/transport/urllib3.py b/google/auth/transport/urllib3.py
index a08f427..0dfe913 100644
--- a/google/auth/transport/urllib3.py
+++ b/google/auth/transport/urllib3.py
@@ -178,16 +178,22 @@
         if http is None:
             http = _make_default_http()
 
-        self.http = http
         self.credentials = credentials
+        self.http = http
         self._refresh_status_codes = refresh_status_codes
         self._max_refresh_attempts = max_refresh_attempts
         # Request instance used by internal methods (for example,
         # credentials.refresh).
         self._request = Request(self.http)
 
+        super(AuthorizedHttp, self).__init__()
+
     def urlopen(self, method, url, body=None, headers=None, **kwargs):
         """Implementation of urllib3's urlopen."""
+        # pylint: disable=arguments-differ
+        # We use kwargs to collect additional args that we don't need to
+        # introspect here. However, we do explicitly collect the two
+        # positional arguments.
 
         # Use a kwarg for this instead of an attribute to maintain
         # thread-safety.