[bug report] popconfirm [bubble confirmation box] when using the in DOM template, v-on cannot listen to the callback event

### Element UI version
2.13.2

### OS/Browsers version
win7 / Chrome

### Vue version
2.6.11

### Reproduction Link
https://codepen.io/8023/pen/PoZpyae?editable=true%3Dhttps%3A%2F%2Felement.eleme.cn%2F

### Steps to reproduce
使用in-DOM模板时不能使用v-on侦听camelCase事件

### What is Expected?
应该使用“ on-confirm”而不是“ onConfirm”。
methods:{
confirm:function(){
this.visible=!1,
this.$emit("on-confirm")
},
cancel:function(){
this.visible=!1,
this.$emit("on-cancel")
}
}

### What is actually happening?
使用in-DOM模板时使用v-on无法侦听到onConfirm事件