Bug 16692 - Error "No method update!" when creating new serial issue

Bug 16692 - Error "No method update!" when creating new serial issue

An improper method call was left over in C4::Serials::NewIssue from the
switch from DBIx::Class to Koha::Object.

Test Plan:
1) prove t/db_dependent/Serials.t
2) Note the errors
3) Apply this patch
4) prove t/db_dependent/Serials.t
5) No errors!

Signed-off-by: Jacek Ablewicz <abl@biblos.pk.edu.pl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>