chore(requirements): update django-auth-ldap to v1.2.11

See http://pythonhosted.org/django-auth-ldap/changes.html#v1-2-11-2017-04-22-testing-and-debugging-cleanup

Author: mboersma

rootfs/requirements.txt

@@ -1,7 +1,7 @@
 # Deis controller requirements
 backoff==1.4.0
 Django==1.11
-django-auth-ldap==1.2.10
+django-auth-ldap==1.2.11
 django-cors-middleware==1.3.1
 django-guardian==1.4.8
 djangorestframework==3.6.2