【Unity】'ZipEntry' could not be f

刚从git上clone下来的项目，报错：

Assets/Plugins/AstarPathfindingProject/Core/Serialization/JsonSerializer.cs(486,3): error CS0246: The type or namespace name 'ZipEntry' could not be found (are you missing a using directive or an assembly reference?)

Assets/Plugins/AstarPathfindingProject/Core/Serialization/JsonSerializer.cs(15,19): error CS0234: The type or namespace name 'Ionic' does not exist in the namespace 'Pathfinding' (are you missing an assembly reference?)

没有.net环境，下载安装一个