[Bug Report] TypeError: escape is not a function

### VUX version
2.9.4

### OS/Browsers version
chrome 版本 74.0.3729.169（正式版本） （64 位）

### Vue version
2.6.10

### Code

```html
import { querystring } from 'vux'

let data = {paramsa: 'xxx'}
querystring.stringify(data)

报错如下：
vue.esm.js?efeb:628 [Vue warn]: Error in mounted hook: "TypeError: escape is not a function"

found in

---> at src/components/PullDownLoad.vue
at node_modules/vux/src/components/view-box/index.vue
at src/components/member/Equity.vue
at src/App.vue

```

### Steps to reproduce
import { querystring } from 'vux'

let data = {paramsa: 'xxx'}
querystring.stringify(data)

### What is Expected?
将对象解析成：
paramsa=xxx

### What is actually happening?
实际行为报错：
vue.esm.js?efeb:628 [Vue warn]: Error in mounted hook: "TypeError: escape is not a function"