perl: add license

pkgs/development/interpreters/perl/default.nix

@@ -152,6 +152,7 @@ let
     meta = {
       homepage = https://www.perl.org/;
       description = "The standard implementation of the Perl 5 programmming language";
+      license = licenses.gpl1;
       maintainers = [ maintainers.eelco ];
       platforms = platforms.all;
     };