AtImagePicker组件，files有默认值的时候，删除图片后无法再选择图片

"@babel/runtime": "^7.7.7",
"@tarojs/cli": "3.0.21",
"@tarojs/components": "3.0.21",
"@tarojs/react": "3.0.21",
"@tarojs/redux": "^2.2.10",
"@tarojs/runtime": "3.0.21",
"@tarojs/taro": "3.0.21",
"react": "^16.10.0",
"react-dom": "^16.10.0",
"react-redux": "^7.2.2",
"redux": "^4.0.5",
"redux-logger": "^3.0.6",
"redux-thunk": "^2.3.0",
"taro-ui": "^3.0.0-alpha.3"

测试代码如下：
```
import React, {Component} from "react";
import { AtImagePicker } from 'taro-ui'

export default class Index extends Component {
constructor (props) {
super(props)
this.state = {
files: [{
url: 'https://jimczj.gitee.io/lazyrepay/aragaki1.jpeg',
},
{
url: 'https://jimczj.gitee.io/lazyrepay/aragaki2.jpeg',
},
{
url: 'https://jimczj.gitee.io/lazyrepay/aragaki3.png',
}]
}

}

onChange (files) {
this.setState({
files
})
}
onFail (mes) {
console.log(mes)
}
onImageClick (index, file) {
console.log(index, file)
}
render () {
return (

)
}
}

```