freeciv: 2.5.11 -> 2.6.0

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools. This update was made based on information from https://repology.org/metapackage/freeciv/versions.

pkgs/games/freeciv/default.nix

···
   inherit (stdenv.lib) optional optionals;
 
   name = "freeciv";
-  version = "2.5.11";
+  version = "2.6.0";
 in
 stdenv.mkDerivation {
   name = "${name}-${version}";
···
 
   src = fetchurl {
     url = "mirror://sourceforge/freeciv/${name}-${version}.tar.bz2";
-    sha256 = "1bcs4mj4kzkpyrr0yryydmn0dzcqazvwrf02nfs7r5zya9lm572c";
+    sha256 = "16f9wsnn7073s6chzbm3819swd0iw019p9nrzr3diiynk28kj83w";
   };
 
   nativeBuildInputs = [ pkgconfig ];