Bug 14624 - <<items.content>> for advance_notices.pl wrongly documented

Bug 14624 - <<items.content>> for advance_notices.pl wrongly documented

To Test Check perldoc for misc/cronjobs/advance_noitces.pl
and see that the documentation matches.

Ran:
$ perldoc misc/cronjobs/advance_noitces.pl
Saw expected changes.
Koha QA test tools pass too.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Switched due date for the name of the database column
date_due as the parameter expects a list of database
column names.