[Bug Report] datatime不能在mounted下初始化值

### VUX version
2.9.2

### OS/Browsers version
mui8/vue的app

### Vue version
2.5.17-beta.0

### Code

```html

export default {
name: 'school',
data () {
return {
time :''
}
},
methods:{
fn(){
this.time = '2017-10-10'
}
},
mounted(){
this.time = '2017-10-10'
}
}

```

### Steps to reproduce
在mounted里面初始化time的值datetime的文本框值没变化，但是点击事件fn却能够改变datetime的文本框值，mounted不可以？这是怎么回事？

### What is Expected?
解决mounted初始化值的问题

### What is actually happening?
无