ranger: works fine on Darwin (close #9454)

pkgs/applications/misc/ranger/default.nix

···
     description = "File manager with minimalistic curses interface";
     homepage = "http://ranger.nongnu.org/";
     license = stdenv.lib.licenses.gpl3;
-    platforms = stdenv.lib.platforms.linux;
+    platforms = stdenv.lib.platforms.unix;
     maintainers = with stdenv.lib.maintainers; [ iyzsong ];
   };