Update Operation System

增加异步操作取消方法

Assets/YooAsset/Runtime/OperationSystem/AsyncOperationBase.cs

@@ -81,6 +81,14 @@ namespace YooAsset
 				_taskCompletionSource.TrySetResult(null);
 		}
 
+		/// <summary>
+		/// 取消异步操作
+		/// </summary>
+		public virtual void Cancel()
+		{
+			throw new NotImplementedException("Can not cancel operation !");
+		}
+
 		#region 异步编程相关
 		bool IEnumerator.MoveNext()
 		{