Add virtual destructor to class with virtual functions but non-virtual destructor

Reviewed By: jdthomas

Differential Revision: D16954508

fbshipit-source-id: 958118843687145c1147ac5beeb2857b21332702

iOS/Plugins/FlipperKitNetworkPlugin/FlipperKitNetworkPlugin/SKDispatchQueue.h

@@ -16,6 +16,7 @@ namespace facebook {
     {
     public:
       virtual void async(dispatch_block_t block) = 0;
+      virtual ~DispatchQueue() { }
     };
 
     class GCDQueue: public DispatchQueue