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

test/unit/adapters/http.js
var axios = require('../../../index');
var http = require('http');
var net = require('net');
var url = require('url');
var zlib = require('zlib');
var assert = require('assert');
var fs = require('fs');
var server, proxy;
describe('supports http with nodejs', function () {
  afterEach(function () {
    if (server) {
      server.close();
      server = null;
    }
    if (proxy) {
      proxy.close()
      proxy = null;
    }
    if (process.env.http_proxy) {
      delete process.env.http_proxy;
    }
    if (process.env.no_proxy) {
      delete process.env.no_proxy;
    }
  });
  it('should respect the timeout property', function (done) {