Error with https://zstack.org/tutorials/flat-network-cli.html

exception = HTTPSConnectionPool(host='zstack.org', port=443): Max retries exceeded with url: /tutorials/flat-network-cli.html (Caused by SSLError(SSLCertVerificationError(1, "[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: Hostname mismatch, certificate is not valid for 'zstack.org'. (_ssl.c:992)")))