Bug 19998: use Modern::Perl in error perl scripts

Test Plan:
Check the following files have been updated from
use strict;
use warnings;
to
use Modern::Perl;

400.pl
401.pl
402.pl
403.pl
404.pl
500.pl

Signed-off-by: Jon Knight <J.P.Knight@lboro.ac.uk>

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

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

errors/400.pl

@@ -16,8 +16,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
 
-use strict;
-use warnings;
+use Modern::Perl;
 use CGI qw ( -utf8 );
 use C4::Auth;
 use C4::Output;

errors/401.pl

@@ -15,8 +15,7 @@
 # Koha; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
-use strict;
-use warnings;
+use Modern::Perl;
 use CGI qw ( -utf8 );
 use C4::Auth;
 use C4::Output;

errors/402.pl

@@ -16,8 +16,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
 
-use strict;
-use warnings;
+use Modern::Perl;
 use CGI qw ( -utf8 );
 use C4::Auth;
 use C4::Output;

errors/403.pl

@@ -16,8 +16,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
 
-use strict;
-use warnings;
+use Modern::Perl;
 use CGI qw ( -utf8 );
 use C4::Auth;
 use C4::Output;

errors/404.pl

@@ -16,8 +16,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
 
-use strict;
-use warnings;
+use Modern::Perl;
 use CGI qw ( -utf8 );
 use C4::Auth;
 use C4::Output;

errors/500.pl

@@ -16,8 +16,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
 
-use strict;
-use warnings;
+use Modern::Perl;
 use CGI qw ( -utf8 );
 use C4::Auth;
 use C4::Output;