Add missing virtual dtors to the TaskQueue class (#54)

Author: an-tao

trantor/utils/SerialTaskQueue.h

@@ -35,7 +35,7 @@ class SerialTaskQueue : public TaskQueue
     void waitAllTasksFinished();
     SerialTaskQueue() = delete;
     explicit SerialTaskQueue(const std::string &name = std::string());
-    ~SerialTaskQueue();
+    virtual ~SerialTaskQueue();
     bool isRuningTask()
     {
         return _loopThread.getLoop()

trantor/utils/TaskQueue.h

@@ -39,5 +39,8 @@ class TaskQueue : public NonCopyable
         });
         fut.get();
     };
+    virtual ~TaskQueue()
+    {
+    }
 };
 }  // namespace trantor