ddnet: 20.0 -> 20.1.1
https://ddnet.org/downloads/#20.1.1
https://github.com/ddnet/ddnet/compare/20.0...20.1.1
also add myself as maintainer as offered in https://github.com/NixOS/nixpkgs/pull/557747#issuecomment-5464310186
(cherry picked from commit 602483c48d525c777ccf634a74b53f3e3e9a6971)