[Bug Report] location.search 报错

### VUX version
0.1.0

### OS/Browsers version
win7/google 66.0.3359.139

### Vue version
2.6.10

### Code

```html
// node_modules\vux\src\tools\querystring\index.js

var unescape = unescape;

for (var i = 0; i < pairs.length; i ) {

var pair = pairs[i].split(eq);
var key = unescape(trim(pair[0]));
var val = unescape(trim(pair.slice(1).join(eq)));

var m = key.match(/^(\w )\[\]$/);
if (m && m[1]) {
key = m[1];
}

if (hasOwnProperty.call(ret, key)) {
if (!isArray(ret[key])) {
ret[key] = [ret[key]];
}
ret[key].push(val);
} else {
ret[key] = m ? [val] : val;
}
}
```

### Steps to reproduce
在网页中任意位置使用location.search 报错，unescape未定义

### What is Expected?
组件不影响正常的浏览器行为

### What is actually happening?
凡是拥有location.search的页面都报错了