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
lib/adapters/http.js
if (proxyUrl) {
        var parsedProxyUrl = url.parse(proxyUrl);
        proxy = {
          host: parsedProxyUrl.hostname,
          port: parsedProxyUrl.port
        };
        if (parsedProxyUrl.auth) {
          var proxyUrlAuth = parsedProxyUrl.auth.split(':');
          proxy.auth = {
            username: proxyUrlAuth[0],
            password: proxyUrlAuth[1]
          };
        }
      }
    }
    if (proxy) {
      options.hostname = proxy.host;
      options.host = proxy.host;
      options.headers.host = parsed.hostname + (parsed.port ? ':' + parsed.port : '');
      options.port = proxy.port;
      options.path = protocol + '//' + parsed.hostname + (parsed.port ? ':' + parsed.port : '') + options.path;
      
      if (proxy.auth) {
        var base64 = new Buffer(proxy.auth.username + ':' + proxy.auth.password, 'utf8').toString('base64');
        options.headers['Proxy-Authorization'] = 'Basic ' + base64;
      }
    }
    var transport;
    if (config.maxRedirects === 0) {
      transport = isHttps ? https : http;