Originally this was manually applied with;
```sh
nixpkgs-fmt **.nix && statix fix
```
but I overlooked the fact that `**.nix` would only expand to files in
the root (I should have used `**/*.nix`).
Previous commit adds `nix fmt` support which passes `.` to `nixpkgs-fmt`
(if no other path is explicitly specified when running `nix fmt`).
This commit includes the changes made by running `nix fmt`.
