added virtual dtor to polymorphic class template ParseTreeProperty

runtime/Cpp/runtime/src/tree/ParseTreeProperty.h

@@ -29,6 +29,7 @@ namespace tree {
   template<typename V>
   class ANTLR4CPP_PUBLIC ParseTreeProperty {
   public:
+    virtual ~ParseTreeProperty() {}
     virtual V get(ParseTree *node) {
       return _annotations[node];
     }