this.proxy 丢失headers内容
在使用 `this.proxy('http://jsonplaceholder.typicode.com/users?_page=1')` 时，发现直接调用中返回的
```
headers: {
Access-Control-Allow-Credentials:true
Access-Control-Expose-Headers:X-Total-Count, Link
Cache-Control:public, max-age=14400
CF-Cache-Status:REVALIDATED
CF-RAY:33305cd0d6872246-LAX
Connection:keep-alive
Date:Sat, 18 Feb 2017 09:13:21 GMT
Etag:W/"160d-MxiAGkI3ZBrjm0xiEDfwqw"
Expires:Sat, 18 Feb 2017 13:13:21 GMT
Link:
Pragma:no-cache
Server:cloudflare-nginx
Vary:Accept-Encoding
Via:1.1 vegur
X-Content-Type-Options:nosniff
X-Powered-By:Express
X-Total-Count:10
}
```

而 this.proxy 的返回只有这些
```
headers: {
Connection:keep-alive
Content-Encoding:gzip
Content-Type:application/json; charset=utf-8
Date:Sat, 18 Feb 2017 09:05:13 GMT
set-cookie:__cfduid=d8215742543560aabf718ebc4a66c415f1487408713; expires=Sun, 18-Feb-18 09:05:13 GMT; path=/; domain=.typicode.com; HttpOnly
Transfer-Encoding:chunked
Vary:Accept-Encoding
}
```

请问该怎么解决这个问题