traitor: mark as Linux-only

It's in the description of the package: "Automatic Linux privilege
escalation".

pkgs/tools/security/traitor/default.nix

···
   vendorSha256 = null;
 
   meta = with lib; {
-    broken = stdenv.isDarwin;
     description = "Automatic Linux privilege escalation";
     longDescription = ''
       Automatically exploit low-hanging fruit to pop a root shell. Traitor packages
···
       (including most of GTFOBins) in order to pop a root shell.
     '';
     homepage = "https://github.com/liamg/traitor";
+    platforms = platforms.linux;
     license = with licenses; [ mit ];
     maintainers = with maintainers; [ fab ];
   };