config(flake.nix): Switch from nixpkgs-unstable to nixpkgs in terranix

Since we are currently having problems with using nixpkgs-unstable in terranix - we are getting back to the stable version (maybe temporarily)

Author: galin-s

flake.lock

@@ -167,7 +167,7 @@
     terranix = {
       url = "github:terranix/terranix";
       inputs = {
-        nixpkgs.follows = "nixpkgs-unstable";
+        nixpkgs.follows = "nixpkgs";
       };
     };