Update client.py

Author: pmoosh

docker/client.py

@@ -901,7 +901,7 @@ def pull(self, repository, tag=None, stream=False,
                     # auth_config needs to be a dict in the format used by
                     # auth.py username , password, serveraddress, email
                     headers['X-Registry-Auth'] = auth.encode_header(
-                        auth_config)
+                        authcfg)
             else:
                 headers['X-Registry-Auth'] = auth.encode_header(auth_config)