Fix Cannot install with auth proxy.

Fix cannot install with auth proxy.
```javascript
options.headers['Proxy-Authorization'] = 'Basic ' + new Buffer(proxy.auth).toString('base64')
```

This code works with HTTP only. Authentication does not work with HTTPS. Since the CDN has changed from HTTP to HTTPS, the installation is no longer.

[Request function has `proxy` option.](https://github.com/mikeal/request#requestoptions-callback) To work with proxy authentication over HTTPS if it used.

```
options.proxy = proxyUrl
```