zlib.src: shuffle download URLs
zlib.src: shuffle download URLs

On sourceforge I see only versions up to 1.2.11:
  https://sourceforge.net/projects/libpng/files/zlib/
and the order is switched to avoid captcha (I didn't encounter it):
  https://github.com/NixOS/nixpkgs/pull/196167#issuecomment-1280333184

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs