feat: upgrade nix

configs/nix.nix

@@ -7,9 +7,8 @@
       (import <stockholm/krebs/5pkgs>)
     ];
   };
-  # enable `nix flake`
   nix = {
-    package = pkgs.nix;
-    # extraOptions = "experimental-features = nix-command flakes";
+    package = pkgs.nixUnstable;
+    extraOptions = "experimental-features = nix-command flakes";
   };
 }

deploy.nix

@@ -1,9 +1,13 @@
 let
-  krops = builtins.fetchGit (gitFromJson .versions/krops.json);
+  importJson = (import <nixpkgs/lib>).importJSON;
+
+  krops = let kropsVersion = importJson .versions/krops.json; in builtins.fetchGit {
+    rev = kropsVersion.rev;
+    url = kropsVersion.url;
+  };
   lib = import "${krops}/lib";
   pkgs = import "${krops}/pkgs" {};
 
-  importJson = (import <nixpkgs> {}).lib.importJSON;
   gitFromJson = path:
     let
       object = importJson path;

shell.nix

@@ -1,9 +1,8 @@
 { pkgs ? import <nixpkgs> { }
+, lib ? import <nixpkgs/lib>
 , release ? "21.11"
 }:
 let
-  inherit (pkgs) lib;
-
   dependencies = {
     nixpkgs = {
       ref = "refs/heads/nixos-${release}";
@@ -73,7 +72,7 @@ in pkgs.mkShell {
     (let
       deployCommand = pkgs.writers.writeDash "niveum-deploy-one" ''
         ${pkgs.git}/bin/git diff $(${pkgs.openssh}/bin/ssh "$1" cat /etc/niveum/version)
-        eval "$(${pkgs.nix}/bin/nix-build --no-out-link "${toString ./.}/deploy.nix" -A "$1")"
+        eval "$(${pkgs.nixUnstable}/bin/nix-build --no-out-link "${toString ./.}/deploy.nix" -A "$1")"
       '';
     in pkgs.writers.writeDashBin "niveum-deploy" ''
       deploy() {