add auth_type default to InvitedUser object

we unpack the api invited user rest endpoint results straight into the
InvitedUser object, so we should make sure that any fields added to
the api response are mentioned here

app/notify_client/models.py

@@ -141,7 +141,7 @@ class User(UserMixin):
 
 class InvitedUser(object):
 
-    def __init__(self, id, service, from_user, email_address, permissions, status, created_at):
+    def __init__(self, id, service, from_user, email_address, permissions, status, created_at, auth_type=None):
         self.id = id
         self.service = str(service)
         self.from_user = from_user