gel.demo: Use 'gel_sdl'.

4-high/gel/applet/demo/sprite/drop_ball_on_box/drop_ball_on_box.gpr

@@ -1,7 +1,8 @@
 with
-     "gel",
+     "gel_sdl",
      "lace_shared";
 
+
 project Drop_Ball_On_Box
 is
    for Object_Dir use "build";
@@ -19,4 +20,4 @@ is
       for Linker_Options use ("-g", "-lGL", "-lGLU", "-lglut", "-lSDL2");   
    end Linker;
 
-end Drop_Ball_On_Box;
+end Drop_Ball_On_Box;