update

global/system-configuration.nix

@@ -56,7 +56,8 @@ in
     };
   };
 
-  nix.settings = {
+  nix = {
+    settings = {
       auto-optimise-store = true;
       experimental-features = [
         "nix-command"
@@ -78,9 +79,10 @@ in
       ];
     };
 
-  nix.gc = {
+    gc = {
       automatic = true;
       dates = "weekly";
       options = "--delete-older-than 1w";
     };
+  };
 }