Add unzip requirement

Change-Id: I957e19257f7be8e2840d80a2abbec8b39dbc060c
diff --git a/t/script/serial.t b/t/script/serial.t
index a4a64f1..00e5559 100644
--- a/t/script/serial.t
+++ b/t/script/serial.t
@@ -5,11 +5,16 @@
 use File::Basename 'dirname';
 use File::Spec::Functions qw/catdir catfile/;
 use File::Temp qw/:POSIX/;
+use KorAP::XML::Archive;
 
 if ($ENV{SKIP_SCRIPT}) {
   plan skip_all => 'Skip script tests';
 };
 
+unless (KorAP::XML::Archive::test_unzip) {
+  plan skip_all => 'unzip not found';
+};
+
 my $f = dirname(__FILE__);
 my $script = catfile($f, '..', '..', 'script', 'korapxml2krill');