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
test.equal(res.data, 'Basic ' + base64);
        test.done();
      });
    });
  },
  testMaxContentLength: function(test) {
    var str = Array(100000).join('ж');
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'text/html; charset=UTF-8');
      res.end(str);
    }).listen(4444, function () {
      var success = false, failure = false, error;
      axios.get('http://localhost:4444/', {
        maxContentLength: 2000
      }).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.message, 'maxContentLength size of 2000 exceeded');
        test.done();
      }, 100);
    });
  },
  testStream: function(test) {
    server = http.createServer(function (req, res) {