Added missing include (why did it work on my computer?)

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/branches/irrlicht@3771 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/guiengine/widgets/ribbon_grid_widget.hpp

@@ -23,7 +23,7 @@
 #include <irrlicht.h>
 
 #include "guiengine/widget.hpp"
-#include "guiengine/ribbon_widget.hpp"
+#include "guiengine/widgets/ribbon_widget.hpp"
 #include "utils/ptr_vector.hpp"
 
 using namespace irr;