update zh-cn/application-dev/ui/arkts-component-animation.md.

Signed-off-by: LiAn <lian15@huawei.com> 
Signed-off-by: NLiAn <lian15@huawei.com>

zh-cn/application-dev/ui/arkts-component-animation.md

@@ -279,7 +279,7 @@ export struct TaskSwitchMainPage {
               .translate({ x: this.cardOffset })
               .animation({ curve: curves.springMotion() })
               .zIndex((this.getProgress(index) >= 0.4 && this.getProgress(index) <= 0.6) ? 2 : 1)
-          }, item => item)
+          }, item => item.index)
         }
         .width((this.cardWidth + this.cardSpace) * (taskDataArr.length + 1))
         .height('100%')