check-builtin-literals: Appease flake8 with six

testing/resources/builtin_constructors.py

diff --git a/testing/resources/builtin_constructors.py b/testing/resources/builtin_constructors.py
index 720bd2b..174a9e8 100644
--- a/testing/resources/builtin_constructors.py
+++ b/testing/resources/builtin_constructors.py
@@ -1,5 +1,4 @@
-# flake8 checks imports; `builtins` does not exist in Python 2.
-# flake8: noqa
+from six.moves import builtins
 
 c1 = complex()
 d1 = dict()