Update Thread.php

This is probably wrong, and we don't have Poll part yet

src/Discord/Parts/Thread/Thread.php

@@ -70,6 +70,8 @@
  * @property      int|null      $total_message_sent    Number of messages ever sent in a thread, it's similar to `message_count` on message creation, but will not decrement the number when a message is deleted.
  * @property      int|null      $flags                 Channel flags combined as a bitfield. PINNED can only be set for threads in forum channels.
  * @property      string[]|null $applied_tags          The IDs of the set of tags that have been applied to a thread in a forum channel, limited to 5.
+ * @property      Poll|null     $poll                  One of content, file, embeds, poll
+ *
  *
  * @property MessageRepository $messages Repository of messages sent in the thread.
  * @property MemberRepository  $members  Repository of members in the thread.