cpanfile: Use url instead mirror for Geography::NationalGrid

[thibaultduponchelle]

Description

mirror => is failing (for carton install, not sure about carton install --deployment) with recent carton/cpanm and I doubt it works with old vendored carton neither.

I propose to replace per url => which is documented (mirror is documented but only with usage of dist along).

What do you think?

Please check the following:

• Have you updated the changelog? If this is not necessary, put square brackets around this: [skip changelog]

[dracos]

I've just run our vendored carton on a fresh install with --deployment, and without --deployment and Geograph::NationalGrid installed in both cases, at least - I think it might use the snapshot information if present regardless?
(Separately, it looks like there's an issue with XML::LibXML needing upgrading).

Happy to change the line if it doesn't work with more recent versions though, of course, as long as it doesn't break our vendored version.

[thibaultduponchelle]

Yes it's using the cpanfile.snapshot infos even without --deployment

What gives you a clean run ./vendor/bin/carton install after removing local/ and cpanfile.snapshot?