chore(requirements): update Django to 1.11 LTS

See https://www.djangoproject.com/weblog/2017/apr/04/django-111-released/

Author: mboersma

rootfs/requirements.txt

@@ -1,6 +1,6 @@
 # Deis controller requirements
 backoff==1.4.0
-Django==1.10.6
+Django==1.11
 django-auth-ldap==1.2.10
 django-cors-middleware==1.3.1
 django-guardian==1.4.6