chore(requirements): update pyldap to v2.4.35

From the CHANGES doc at https://github.com/pyldap/pyldap/blob/master/CHANGES:

----------------------------------------------------------------
Released 2.4.35 2017-04-25 (upstream)

Changes since 2.4.33:
(2.4.34 is missing because of foolish pypi version madness)

Modules/
* use errno in a safer way
* set errno as LDAPError class item
* do not use strerror() which is not thread-safe and platform-specific

Lib/
* LDAPObject._ldap_call() sets LDAPError info to value returned
  by platform-neutral os.stderror()

Author: mboersma

rootfs/requirements.txt

@@ -16,7 +16,7 @@ ndg-httpsclient==0.4.2
 packaging==16.8
 pyasn1==0.2.3
 psycopg2==2.7.1
-pyldap==2.4.28
+pyldap==2.4.35
 pyOpenSSL==17.0.0
 pytz==2017.2
 requests==2.13.0