Update pre-commit config to enforace that future imports exist in all files.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

tests/unit/cli/command_test.py

@@ -1,4 +1,5 @@
 from __future__ import absolute_import
+from __future__ import unicode_literals
 
 import pytest
 from requests.exceptions import ConnectionError