Core: Fixed compile without PCH

src/server/game/Entities/Unit/StatSystem.cpp

@@ -24,6 +24,7 @@
 #include "SpellAuras.h"
 #include "SpellAuraEffects.h"
 #include "SpellMgr.h"
+#include "World.h"
 
 inline bool _ModifyUInt32(bool apply, uint32& baseValue, int32& amount)
 {