Make DataLibrary destructor virtual.

src/Library/DataLibrary.hpp

@@ -26,7 +26,7 @@ namespace CreatureLib::Library {
                     CreatureLib::Library::AttackLibrary* attacks, CreatureLib::Library::ItemLibrary* items,
                     CreatureLib::Library::GrowthRateLibrary* growthRates, TypeLibrary* typeLibrary);
 
-        ~DataLibrary() {
+        virtual ~DataLibrary() {
             delete _species;
             delete _attacks;
             delete _items;