Update ext.nce_ldap.php

In EE 2.5.5 Developer Log:
The system has detected an add-on that is using outdated code that may stop working or cause issues with the system. What does this mean?
Deprecated function hash() called in /system/expressionengine/third_party/nce_ldap/ext.nce_ldap.php on line 246.
Deprecated since 2.0. Use Security_helper::do_hash instead.