Do not use v-for index as key on ＜transition-group＞ children, this is the same as not using keys.

(Emitted value instead of an instance of Error) Do not use v-for index as key on <transition-group> children, this is the same as not using keys.

如：将v-for="(item,index) in list"的:key="index"，改为:key="item.id"