[Bug Report] Wrong El-Select > El-Input value

### Element UI version
2.5.4

### OS/Browsers version
/

### Vue version
2.6.6

### Reproduction Link
[https://jsfiddle.net/gkL60m4p/](https://jsfiddle.net/gkL60m4p/)

### Steps to reproduce
```html

```

```javascript
var Main = {
data() {
return {
post: { status: 1 },
list: [
{ value: 1, label: 'one' },
{ value: 2, label: 'two' },
{ value: 3, label: 'three' },
],
}
}
}
```

### What is Expected?
document.getElementById('app').status.value === 1

### What is actually happening?
document.getElementById('app').status.value === 'one'