Forgot to use branches, remember kids: use protection

I'd like less generations please side note:
it's a bit weird that you can't specify how many generations you'd like
to keep, like what if I want 3 generations to stay available?

modules/os.nix

@@ -10,7 +10,7 @@
       dates = "weekly";
       automatic = true;
       randomizedDelaySec = "45min";
-      options = "--delete-older-than 30d";
+      options = "--delete-older-than 7d";
     };
   };