anchor.diff:  
   mkDerivation rec {
     name = "quaternion-git-${version}";
  -  version = "2017-04-15";
  +  version = "2017-06-29";
   
     # quaternion and tensor share the same libqmatrixclient library as a git submodule
     #
  
positive.code:   # derivation.
  
    src = fetchgit {
      url             = "https://github.com/Fxrh/Quaternion.git";
      rev             = "c35475a6755cdb75e2a6c8ca5b943685d07d9707";
      sha256          = "0cm5j4vdnp5cljfnv5jqf89ccymspaqc6j9bb4c1x891vr42np0m";
      fetchSubmodules = true;
    };
  
  
negative.code:   postInstall = ''
      substituteInPlace $out/share/applications/quaternion.desktop \
        --replace 'Exec=quaternion' "Exec=$out/bin/quaternion"
    '';
  
    meta = with lib; {
      description = "Cross-platform desktop IM client for the Matrix protocol";
      homepage    = https://matrix.org/docs/projects/client/quaternion.html;
      license     = licenses.gpl3;
      maintainers = with maintainers; [ peterhoeg ];
      inherit (qtbase.meta) platforms;
      inherit version;
  