Bug 24447: Changing 'DUE' to example in database that exists.

Bug 24447: Changing 'DUE' to example in database that exists.

Test Plan:
1.Using  perldoc C4/Members/Messaging.pm check that message_name
attribute name example  is Item_Due and not DUE.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 0a0ff7c5ceab836631be060a4571681ff40e275c)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit 9c4aeca752210bbb504a84d84dbe49a9394ff0a3)

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>