Handle the urllist option when using CPAN

This is a local change that I've needed working with [Pinto](https://metacpan.org/pod/Pinto) and not wanting to maintain a fork I thought I'd push it upstream :smile:. Not sure of an appropriate way to test it but I'm hoping the change is sufficiently simple that it isn't necessary. Usage in a `Makefile.PL` postamble looks something like this:

```shell
$(PERL) Makefile.PL --config=urllist,$(PINTO_URL)/$(BRANCH) --installdeps=...
```

Cheers,
Dan Brook