Update redirector to always use latest version of nix.dev

[quatquatt]

nix.dev has multiple versions of the Nix reference manual, depending on the version. Some older links use a specific version, which is unhelpful for finding the latest info on something. To fix this, links should be redirected to the latest stable version. Here's how this can be done:

Old link:

https://nix.dev/manual/nix/2.12/installation/multi-user

New link:

https://nix.dev/manual/nix/latest/installation/multi-user

Ideally, this would automatically fail if the new link didn't exist. I'm not sure if Redirector supports this, though.

[quatquatt]

Done with this file: Redirector.json