nix-generate-from-cpan: strip leading v from versions

Everything currently in perl-packages.nix already does this,
so we might as well automate it.

maintainers/scripts/nix-generate-from-cpan.pl

···
 
 sub get_pkg_name {
     my ($module) = @_;
-    return ( $module->package_name, $module->package_version );
+    return ( $module->package_name, $module->package_version =~ s/^v(\d)/$1/r );
 }
 
 sub read_meta {