Hi,

I'm using axios v0.17.0 with HEAD method like this:

`axios.head('http://example.com'); `

(let's suppose http://example.com is set to redirect 301 to http://www.example.com)

For some reason Request method will change on the first redirect to GET instead of keeping HEAD all the way down. This will read in logs like this:

```
example.com:80 10.0.0.1 - - "HEAD / HTTP/1.1" 301 237 "-" "axios/0.17.0"
example.com:80 10.0.0.1 - - "GET / HTTP/1.1" 200 246 "-" "axios/0.17.0"
```

instead of this:

```
example.com:80 10.0.0.1 - - "HEAD / HTTP/1.1" 301 237 "-" "axios/0.17.0"
example.com:80 10.0.0.1 - - "HEAD / HTTP/1.1" 200 246 "-" "axios/0.17.0"
```

When I do the test in Firefox it keeps original request method (HEAD) all the way down.

Any idea why is this?

Thanks,
Milos

lib/adapters/http.js
options.maxRedirects = config.maxRedirects;
      }
      transport = isHttpsProxy ? httpsFollow : httpFollow;
    }
    if (config.maxContentLength && config.maxContentLength > -1) {
      options.maxBodyLength = config.maxContentLength;
    }
    
    var req = transport.request(options, function handleResponse(res) {
      if (req.aborted) return;
      
      var stream = res;
      switch (res.headers['content-encoding']) {
      
      case 'gzip':
      case 'compress':
      case 'deflate':
        
        stream = stream.pipe(zlib.createUnzip());
        
        delete res.headers['content-encoding'];
        break;
      }
      
      var lastRequest = res.req || req;
      var response = {
        status: res.statusCode,
        statusText: res.statusMessage,
        headers: res.headers,
        config: config,