EasyRefresh 里不能使用 SizeCacheWidget

[shr871217]

错误提示是：
======== A RenderSliverToBoxAdapter expected a child of type RenderBox but received a child of type RenderSliverList. RenderObjects expect specific types of children because they coordinate with their children during layout and paint. For example, a RenderSliver cannot be the child of a RenderBox because a RenderSliver does not understand the RenderBox layout protocol.

加上SizeCacheWidget 后就会走上图的分支里