Bug 19968: Add missing use Date::Calc statement

It has been reported than the missing use statement can cause a
compilation error:
Undefined subroutine &Date::Calc::Today called at
/usr/share/koha/intranet/cgi-bin/cataloguing/value_builder/unimarc_field_100.pl
line 75.

Test plan:
Use this UNIMARC plugin and make sure it fixes the error or at least
does not break it

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

cataloguing/value_builder/unimarc_field_100.pl

@@ -20,6 +20,7 @@
 
 use strict;
 #use warnings; FIXME - Bug 2505
+use Date::Calc qw( Today );
 
 use Koha::Util::FrameworkPlugin qw(wrapper);
 use C4::Auth;