Fix create_container environment parameter for python3

docker/client.py

@@ -115,8 +115,8 @@ class Client(requests.Session):
             command = shlex.split(str(command))
         if isinstance(environment, dict):
             environment = [
-                (six.text_type('{0}={1}').format(k, v)
-                    for k, v in environment.items())
+                six.text_type('{0}={1}').format(k, v)
+                for k, v in six.iteritems(environment)
             ]
 
         if isinstance(mem_limit, six.string_types):