[Bug Report] quertstring stringify/parse出现escape/unescape undefined

### VUX version
2.9.4

### OS/Browsers version
macos

### Vue version
2.6.10

### Code

```html

import { querystring } from 'vux'
console.log(querystring.parse())
export default {
filters: {
querystring
}
}

```

### Steps to reproduce
运行demo/querystring.vue 即可，提示escape is not a function或者unescape is not a function，

### What is Expected?
修复querystring/index.js, stringify和parse中不使用变量escape/unescape即可

### What is actually happening?
提示escape is not a function或者unescape is not a function