add virtual destructor to feature for polymorphism

src/feature.cpp

@@ -12,3 +12,5 @@ char Feature::getSymbol() {
 Coord Feature::getLocation() {
 	return this->location;
 }
+
+Feature::~Feature() {}

src/include/feature.h

@@ -7,6 +7,7 @@ class Feature {
 		Feature(char, Coord);
 		char getSymbol();
 		Coord getLocation();
+		virtual ~Feature();
 	private:
 		Coord location;
 		char symbol;