更新完 Flarum 扩展，执行 php flarum migrate 提示 SQLSTATE[42000]: Syntax error or access violation: 1091 Can’t DROP polls_discussion_id_foreign
; check that column/key exists (SQL: alter table polls drop foreign key polls_discussion_id
_foreign) 这类错误，原因是新版 fof/polls 的问题，需要卸载，重新安装，然后执行 php flarum migrate 和 php flarum cache:clear 问题一般能解决。
In Connection.php line 712:
In Connection.php line 712:
SQLSTATE[42000]: Syntax error or access violation: 1091 Can't DROP 'polls_discussion_id_foreign
'; check that column/key exists (SQL: alter table `polls` drop foreign key `polls_discussion_id
_foreign`)
In Exception.php line 18:
SQLSTATE[42000]: Syntax error or access violation: 1091 Can't DROP 'polls_discussion_id_foreign
'; check that column/key exists
In PDOStatement.php line 117:
SQLSTATE[42000]: Syntax error or access violation: 1091 Can't DROP 'polls_discussion_id_foreign
'; check that column/key exists
