Add default destructor to EmitFromEvents

Author: Levi-Armstrong

include/yaml-cpp/emitfromevents.h

@@ -23,6 +23,7 @@ class Emitter;
 class EmitFromEvents : public EventHandler {
  public:
   EmitFromEvents(Emitter& emitter);
+  ~EmitFromEvents() override = default;
 
   void OnDocumentStart(const Mark& mark) override;
   void OnDocumentEnd() override;