springlobby: fix build failure

[bobvanderlinden]

Motivation for this change

The build of springLobby was failing. This PR is intended to resolve a hydra failure of 20.09, part of #97479

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[domenkozar]

@GrahamcOfBorg build springLobby

[worldofpeace]

I believe on 20.09 this will be marked broken, so backporting will required to unset that.

[bobvanderlinden]

@worldofpeace do I need to do something to backport this?

[worldofpeace]

Yeah, see CONTRIBUTING.md with how to do that.