In my case I have a `http_proxy` env variable on my development computer which passes all traffic to my vpn, however this proxy would fail to work when hostname is `localhost`, therefore when I'm testing my application it always fails because I setup my server at localhost, I want a method to force axios receiving a `none` for proxy config, currently if `proxy` property is `null` or `undefined` it will use the `http_proxy` env
test/unit/adapters/http.js
res.setHeader('Content-Type', 'text/html; charset=UTF-8');
      res.end(str);
    }).listen(4444, function () {
      axios.get('http://localhost:4444/').then(function (res) {
        test.equal(res.data, str);
        test.done();
      });
    });
  },
  testBasicAuth: function (test) {
    server = http.createServer(function (req, res) {
      res.end(req.headers.authorization);
    }).listen(4444, function () {
      var user = 'foo';
      var headers = { Authorization: 'Bearer 1234' };
      axios.get('http://' + user + '@localhost:4444/', { headers: headers }).then(function (res) {
        var base64 = new Buffer(user + ':', 'utf8').toString('base64');
        test.equal(res.data, 'Basic ' + base64);
        test.done();
      });
    });
  },
  testBasicAuthWithHeader: function (test) {
    server = http.createServer(function (req, res) {
      res.end(req.headers.authorization);
    }).listen(4444, function () {
      var auth = { username: 'foo', password: 'bar' };
      var headers = { Authorization: 'Bearer 1234' };
      axios.get('http://localhost:4444/', { auth: auth, headers: headers }).then(function (res) {
        var base64 = new Buffer('foo:bar', 'utf8').toString('base64');