perl: renamed benchmark script

perl/benchmark/serialize.pl

@@ -7,6 +7,8 @@ use Benchmark ':all';
 my $a = [0..2**24];
 
 print "-- serialize\n";
+print "JSON::XS: $JSON::XS::VERSION\n";
+print "Data::MessagePack: $Data::MessagePack::VERSION\n";
 cmpthese(
     -1 => {
         json => sub { JSON::XS::encode_json($a)   },