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
}
          },
          headers: {
            'Proxy-Authorization': 'Basic abc123'
          }
        }).then(function (res) {
          var base64 = Buffer.from('user:pass', 'utf8').toString('base64');
          assert.equal(res.data, 'Basic ' + base64, 'should authenticate to the proxy');
          done();
        });
      });
    });
  });
  it('should support cancel', function (done) {
    var source = axios.CancelToken.source();
    server = http.createServer(function (req, res) {
      // 
      source.cancel('Operation has been canceled.');
    }).listen(4444, function () {
      axios.get('http://localhost:4444/', {
        cancelToken: source.token
      }).catch(function (thrown) {
        assert.ok(thrown instanceof axios.Cancel, 'Promise must be rejected with a Cancel obejct');
        assert.equal(thrown.message, 'Operation has been canceled.');
        done();
      });
    });
  });
});