elementUI 日期选择报错 Prop being mutated: "placement"......

 报错上图所示，

Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value. Prop being mutated: "placement".......

解决办法  elementUI 换 2.15 版本，element-ui@2.15