sort can't work without const on modern C++

Index: hiscore.h
--- hiscore.h.orig
+++ hiscore.h
@@ -28,7 +28,7 @@ class HiScore (public)
     std::string name;
     int level;
     int points;
-    bool operator<(const HiScore& h) { return points > h.points; };
+    bool operator<(const HiScore& h) const { return points > h.points; };
 };
 //-----------------------------------------------------------------------------
 class HiScores
