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
var success = false, failure = false;
      var error;
      axios.get('http://localhost:4444/', {
        timeout: 250
      }).then(function (res) {
        success = true;
      }).catch(function (err) {
        error = err;
        failure = true;
      });
      setTimeout(function () {
        test.equal(success, false, 'request should not succeed');
        test.equal(failure, true, 'request should fail');
        test.equal(error.code, 'ECONNABORTED');
        test.equal(error.message, 'timeout of 250ms exceeded');
        test.done();
      }, 300);
    });
  },
  testJSON: function (test) {
    var data = {
      firstName: 'Fred',
      lastName: 'Flintstone',
      emailAddr: 'fred@example.com'
    };
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'application/json;charset=utf-8');
      res.end(JSON.stringify(data));
    }).listen(4444, function () {
      axios.get('http://localhost:4444/').then(function (res) {