chore(requirements.txt): update django-guardian to 1.4.1

See https://raw.githubusercontent.com/django-guardian/django-guardian/devel/CHANGES

Author: mboersma

rootfs/requirements.txt

@@ -2,7 +2,7 @@
 #
 Django==1.9.1
 django-cors-headers==1.1.0
-django-guardian==1.3.2
+django-guardian==1.4.1
 djangorestframework==3.3.2
 jsonfield==1.0.3
 docker-py==1.6.0