modules/btop: fix unnecessary rebuilds when flake source changes

Author: adeci

modules/btop/module.nix

@@ -17,7 +17,7 @@
   };
 
   config.flags = {
-    "--config" = toString config."btop.conf".path;
+    "--config" = "${config."btop.conf".path}";
   };
 
   config.package = config.pkgs.btop;