Auto optimize storage

configuration.nix

@@ -65,7 +65,11 @@ in {
   system.stateVersion = "18.09";
   system.autoUpgrade.enable = true;
 
-  nix.gc.automatic = true;
-  nix.gc.dates = "weekly";
-  nix.gc.options = "--delete-older-than 30d";
+  nix = {
+    optimise.automatic = true;
+    gc = {
+      automatic = true;
+      options = "--delete-older-than 7d";
+    };
+  };
 }