docs: function proxy(url, opts) {
    opts = opts || {};
  
    var _proxy;
  
    if (!url) {
      _proxy = process.env.http_proxy || process.env.HTTP_PROXY || process.env.https_proxy || process.env.HTTPS_PROXY;
    } else if (!_proxyIgnored(url, opts)) {
      if (!url.match(/^https?:\/\//)) {
        url += 'http://' + url;
      }
  
      if (url.match(/^https:\/\//)) {
        _proxy = process.env.https_proxy || process.env.HTTPS_PROXY || process.env.http_proxy || process.env.HTTP_PROXY;
      } else {
        _proxy = process.env.http_proxy || process.env.HTTP_PROXY;
      }
    }
  
    return _proxy;
  }