ran python-modernize and isort on files mentioned in INCR-348 (#21017)

cms/urls_dev.py

@@ -3,6 +3,8 @@ URLconf for development-only views.
 This gets imported by urls.py and added to its URLconf if we are running in
 development mode; otherwise, it is ignored.
 """
+from __future__ import absolute_import
+
 from django.conf.urls import url
 
 from contentstore.views.dev import dev_mode