Credentials并未导出,typescript下无法通过编译

使用环境:
node.js, 使用了NODE.JS SDK,版本 7.2.2
sdk 安装方式:
```
yarn add qiniu
```

以下代码是typescript代码
```
import * as qiniu from 'qiniu'
const qiniu_credentials = new qiniu.Credentials(qiniu_ak, qiniu_sk)
```

提示:

Property 'Credentials' does not exist on type 'typeof import("/xxxx/node_modules/qiniu/index")'

