gama: 2.27 -> 2.28

pkgs/applications/science/geometry/gama/default.nix

···
 { stdenv, fetchurl, lib, expat, octave, libxml2, texinfo, zip }:
 stdenv.mkDerivation rec {
   pname = "gama";
-  version = "2.27";
+  version = "2.28";
 
   src = fetchurl {
     url = "mirror://gnu/${pname}/${pname}-${version}.tar.gz";
-    sha256 = "sha256-k4s7TK/ym68v40KDzZoMMxDWFMRnsMuk6V/G9P/jM0E=";
+    sha256 = "sha256-Xcc/4JB7hyM+KHeO32+JlQWUBfH8RXuOL3Z2P0imaxo=";
   };
 
   buildInputs = [ expat ];