style: Switch to nixfmt from nixpkgs-fmt

Most of the ecosystem has moved to this formatter,
and many people configured their editors to autoformat it with this formatter.

Closes: https://git.snix.dev/snix/snix/issues/62
Change-Id: Icf39e7836c91fc2ae49fbe22a40a639105bfb0bd
Reviewed-on: https://cl.snix.dev/c/snix/+/30671
Reviewed-by: Florian Klink <flokli@flokli.de>
Tested-by: besadii
Autosubmit: Ilan Joselevich <personal@ilanjoselevich.com>

third_party/alertmanager-irc-relay/package.nix

@@ -1,7 +1,7 @@
-{ lib
-, buildGoModule
-, fetchFromGitHub
-,
+{
+  lib,
+  buildGoModule,
+  fetchFromGitHub,
 }:
 
 buildGoModule rec {
@@ -17,7 +17,10 @@ buildGoModule rec {
 
   vendorHash = "sha256-KX+TR0n14+95lldF+0KUo5DbqOKpUDaZNuKMBf0KHFQ=";
 
-  ldflags = [ "-s" "-w" ];
+  ldflags = [
+    "-s"
+    "-w"
+  ];
 
   meta = {
     description = "Send Prometheus Alerts to IRC using Webhooks";