When the [bug report] cascade selector is dynamically loaded and multi select mode is enabled, the value of V-model is initialized and cannot be echoed on the page

### Element UI version
2.13.2

### OS/Browsers version
83.0.4103.61（正式版本） （64 位）

### Vue version
2.5.22

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

### Steps to reproduce

let id = 0;

export default {
data() {
return {
value:[ 1, 2, 4 ],
props: {
lazy: true,
lazyLoad (node, resolve) {
const { level } = node;
setTimeout(() => {
const nodes = Array.from({ length: level 1 })
.map(item => ({
value: id,
label: `选项${id}`,
leaf: level >= 2
}));
// 通过调用resolve将子节点数据返回，通知组件数据加载完成
resolve(nodes);
}, 1000);
}
}
};
}
};

### What is Expected?
初始化的值能回显到页面上

### What is actually happening?
初始化的值没有回显到页面上