Popover控制台报警Warning: Can't perform a React state update on an unmounted component

### Description

动态渲染且触发条件为click的Popover，消失后再出现，再尝试触发时，控制台报警Warning: Can't perform a React state update on an unmounted component

### Reproduce Steps

1. 写一个简单的freetest页面
```
import React from 'react';
import {Popover, Tooltip} from 'element-react'
import 'element-theme-default'

class Freetest extends React.Component{
constructor(props){
super(props)
this.state = {sh : true}
setTimeout(()=>{this.setState({sh:false})}, 2000)
setTimeout(()=>{this.setState({sh:true})}, 4000)
}
render(){
return (

export {Freetest}
```
2.渲染
``

### Error Trace (if possible)

index.js:1375 Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.
in Popover (at free_test.js:17)

### Solution

照着上面的代码，创建一个以click触发的消失又出现的popover元素，然后尝试用鼠标去打开Popover，然后控制台就会报警