nix config to save some space

nixos/roles/nix.nix

@@ -1,6 +1,5 @@
 {
-  nix = {
-    settings = {
+  nix.settings = {
     trusted-public-keys = [
       "nerflap2-1:pDZCg0oo9PxNQxwVSQSvycw7WXTl53PGvVeZWvxuqJc="
       "gonne.mathebau.de-1:FsXFyFiBFE/JxC9MCkt/WuiXjx5dkRI9RXj0FxOQrV0="
@@ -11,7 +10,7 @@
     ];
     auto-optimise-store = true;
     fallback = true;
-      builders-use-substitutes = true;
+    builders-use-substitus = true;
   };
   gc = {
     persistent = true;
@@ -23,5 +22,4 @@
     dates = [];
     automatic = true;
   };
-  };
 }