Fix mailing archive link in CONTRIBUTING.md

Description

Currently in CONTRIBUTING.md mailing archive link goes to "Page not found" page.

I believe the correct URL for this is: https://lists.archlinux.org/mailman3/lists/aur-dev.lists.archlinux.org/

Specifically, this line: [1]: https://lists.archlinux.org/listinfo/aur-dev

Should be changed to: [1]: https://lists.archlinux.org/mailman3/lists/aur-dev.lists.archlinux.org/