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
});
  });
  it('should support transparent gunzip', function (done) {
    var data = {
      firstName: 'Fred',
      lastName: 'Flintstone',
      emailAddr: 'fred@example.com'
    };
    zlib.gzip(JSON.stringify(data), function (err, zipped) {
      server = http.createServer(function (req, res) {
        res.setHeader('Content-Type', 'application/json;charset=utf-8');
        res.setHeader('Content-Encoding', 'gzip');
        res.end(zipped);
      }).listen(4444, function () {
        axios.get('http://localhost:4444/').then(function (res) {
          assert.deepEqual(res.data, data);
          done();
        });
      });
    });
  });
  it('should support gunzip error handling', function (done) {
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'application/json;charset=utf-8');
      res.setHeader('Content-Encoding', 'gzip');
      res.end('invalid response');
    }).listen(4444, function () {
      axios.get('http://localhost:4444/').catch(function (error) {
        done();
      });