Fix flake8 warnings

synapse/handlers/auth.py

@@ -336,7 +336,9 @@ class AuthHandler(BaseHandler):
         m.add_first_party_caveat("type = refresh")
         # Important to add a nonce, because otherwise every refresh token for a
         # user will be the same.
-        m.add_first_party_caveat("nonce = %s" % stringutils.random_string_with_symbols(16))
+        m.add_first_party_caveat("nonce = %s" % (
+            stringutils.random_string_with_symbols(16),
+        ))
         return m.serialize()
 
     def _generate_base_macaroon(self, user_id):