Update nix.gc module with same indenting/formatting as NixOS module

modules/services/nix-gc/default.nix

@@ -1,4 +1,6 @@
-{ config, lib, pkgs, ... }:
+# Based off: https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/misc/nix-gc.nix
+# When making changes please try to keep it in sync.
+{ config, lib, ... }:
 
 with lib;
 
@@ -7,36 +9,48 @@ let
 in
 
 {
+
+  ###### interface
+
   options = {
-    nix.gc.automatic = mkOption {
+
-      type = types.bool;
+    nix.gc = {
-      default = false;
+
-      description = "Automatically run the garbage collector at a specific time.";
+      automatic = mkOption {
+        type = types.bool;
+        default = false;
+        description = "Automatically run the garbage collector at a specific time.";
+      };
+
+      user = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = "User that runs the garbage collector.";
+      };
+
+      interval = mkOption {
+        type = types.attrs;
+        default = { Hour = 3; Minute = 15; };
+        description = "The time interval at which the garbage collector will run.";
+      };
+
+      options = mkOption {
+        type = types.str;
+        default = "";
+        example = "--max-freed $((64 * 1024**3))";
+        description = ''
+          Options given to <filename>nix-collect-garbage</filename> when the
+          garbage collector is run automatically.
+        '';
+      };
+
     };
 
-    nix.gc.user = mkOption {
-      type = types.nullOr types.str;
-      default = null;
-      description = "User that runs the garbage collector.";
-    };
-
-    nix.gc.interval = mkOption {
-      type = types.attrs;
-      default = { Hour = 3; Minute = 15; };
-      description = "The time interval at which the garbage collector will run.";
-    };
-
-    nix.gc.options = mkOption {
-      type = types.str;
-      default = "";
-      example = "--max-freed $((64 * 1024**3))";
-      description = ''
-        Options given to <filename>nix-collect-garbage</filename> when the
-        garbage collector is run automatically.
-      '';
-    };
   };
 
+
+  ###### implementation
+
   config = mkIf cfg.automatic {
 
     launchd.daemons.nix-gc = {