docs: public static Region region2() {
          return new Builder().
                  region("z2").
                  srcUpHost("up-z2.qiniup.com", "up-dg.qiniup.com", "up-fs.qiniup.com").
                  accUpHost("upload-z2.qiniup.com", "upload-dg.qiniup.com", "upload-fs.qiniup.com").
                  iovipHost("iovip-z2.qbox.me").
                  rsHost("rs-z2.qbox.me").
                  rsfHost("rsf-z2.qbox.me").
                  apiHost("api-z2.qiniu.com").
                  build();
      }