dvdauthor: supports darwin

pkgs/applications/video/dvdauthor/default.nix

···
     description = "Tools for generating DVD files to be played on standalone DVD players";
     homepage = http://dvdauthor.sourceforge.net/;
     license = licenses.gpl2;
-    platforms = platforms.linux;
+    platforms = platforms.linux ++ platforms.darwin;
   };
 }