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
http.get(opts, function(res) {
          var body = '';
          res.on('data', function(data) {
            body += data;
          });
          res.on('end', function() {
            response.setHeader('Content-Type', 'text/html; charset=UTF-8');
            response.end(proxyAuth);
          });
        });
      }).listen(4000, function() {
        axios.get('http://localhost:4444/', {
          proxy: {
            host: 'localhost',
            port: 4000,
            auth: {
              username: 'user',
              password: 'pass'
            }
          }
        }).then(function(res) {
          var base64 = new Buffer('user:pass', 'utf8').toString('base64');
          test.equal(res.data, 'Basic ' + base64, 'should authenticate to the proxy');
          test.done();
        });
      });
    });
  },
  testHTTPProxyAuthFromEnv: function(test) {
    server = http.createServer(function(req, res) {