mod_cloud_notify_encrypted: Use new 'util.crypto' on Prosody 13.0 This removes the dependency on lua-luaossl when running on Prosody 13.0 (or trunk) which has util.crypto Compatibility with Prosody 0.12 retained but also the dependency

<tr>
  <th>What is {x} {op} {y}?</th><td>
    <input name="captcha_challenge" type="hidden" value="{challenge}">
    <input name="captcha_reply" pattern="[0-9]+" required type="number">
  </td></tr>