[Bug Report] switch component cannot be disabled

### Mint UI version
2.2.2

### OS/Browsers version
chrome 53

### Vue version
2.2.6

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

### Steps to reproduce
```html

```javascript
var vm = new Vue({
el: '#app',
data: {
disabled: true,
input: true,
},
methods: {
clicked: function() { alert('clicked'); },
}
})
```

### What is Expected?
mt-switch be disabled;
mt-button be disabled

### What is actually happening?
only mt-button be disabled;
mt-switch was not be disabled