docs: fix mailing list after migration to mailman3

Closes: #396



Signed-off-by: Leonidas Spyropoulos <artafinde@archlinux.org>

CONTRIBUTING.md

@@ -8,7 +8,7 @@ Before sending patches, you are recommended to run `flake8` and `isort`.
 You can add a git hook to do this by installing `python-pre-commit` and running
 `pre-commit install`.
 
-[1]: https://lists.archlinux.org/listinfo/aur-dev
+[1]: https://lists.archlinux.org/mailman3/lists/aur-dev.lists.archlinux.org/
 [2]: https://gitlab.archlinux.org/archlinux/aurweb
 
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