chore(requirements): update pyldap to 2.4.28

See pyldap/pyldap@pyldap-2.4.25.1...pyldap-2.4.28

Author: mboersma

rootfs/requirements.txt

@@ -15,7 +15,7 @@ morph==0.1.2
 ndg-httpsclient==0.4.2
 packaging==16.8
 psycopg2==2.6.2
-pyldap==2.4.25.1
+pyldap==2.4.28
 pyOpenSSL==16.2.0
 pytz==2016.10
 requests==2.12.5