[Bug Report] element-ui的Notification 在svg中提供{message:VNode} 无法渲染

### Element UI version
2.13.2

### OS/Browsers version
windows 10

### Vue version
2.6.4

### Reproduction Link
https://codepen.io/pen

### Steps to reproduce
http://jsrun.net/LKIKp
Reproduction Link is not support jsrun , that is false

// parent.vue


// child.vue

123

export default {
mounted() {
let h = this.$createElement;
this.$notify({
title: `the VNode get in this way ,ns is "svg"`,
message: h("div", null, [h("span", null, 123), h("button", null, 123)]),
// message:<div><span>123</span><button>123</button> //is wrong too in jsx
});
//only show title
},
};

reason:
在child.vue中的createElement会记录下来父节点的tagName，比如本例中父组件是svg，vue限制了svg下不能放非法tag名

解决方法:
将父组件的$createElement以props的方式传到child.vue中
手动修改子组件创建出来的VNode的属性，让vue知道他不是svg的子组件

如果有不对请指出，谢谢维护 。 English is not good, I will not translate

### What is Expected?
I need him to show "message"

### What is actually happening?
only show title