Add check for member attributes that just contain a uid for the LDAP group synchronization

- the member attribute of groups provided by our company LDAP contains only a the members
  userid prefixed by 'uid=' an not the full dn of the user
  --> the member attribute has to be checked also for this value

lib/gitlab/ldap/group.rb

@@ -42,6 +42,8 @@ module Gitlab
           member_uids.any? { |member_uid| member_uid.downcase == user_uid }
         elsif member_dns.any? { |member_dn| member_dn.downcase == user_dn }
           true
+        elsif member_dns.any? { |member_dn| member_dn.downcase == "uid=" + user_uid }
+          true
         elsif adapter.config.active_directory
           adapter.dn_matches_filter?(user.dn, active_directory_recursive_memberof_filter)
         end