ActivityUpdaterJob->after_action: fix txn conflict
ActivityUpdaterJob->after_action: fix txn conflict

Creating a post would update thredded user detail (incr post count),
but so does ActivityUpdaterJob (update last_seen_at).

If these happen the same time on SQLite3, the following error is thrown:

  SQLite3::BusyException: database is locked

Moving the schedule to after_action prevents this.

thredded/thredded,jayroh/thredded,jvoss/thredded,jvoss/thredded,thredded/thredded,jvoss/thredded,jayroh/thredded,jayroh/thredded,jayroh/thredded,thredded/thredded,thredded/thredded,jvoss/thredded