Use dispatch method instead of fire method.

[xharpenParksuhyeon]

https://laravel.com/docs/5.8/upgrade#events

The fire Method
Likelihood Of Impact: Low

The fire method (which was deprecated in Laravel 5.4) of the Illuminate\Events\Dispatcher class [has been removed](https://github.com/laravel/framework/pull/26392). You should use the dispatch method instead.

Event::fire Method가 삭제되고 Event::dispatch 메소드를 사용되도록 라라벨 코어가 수정되었습니다.

라라벨 5.5 버전에도 Event::dispatch 메소드는 지원되고 있는 걸 확인했습니다.
그래서 fire 메소드를 사용하고 있는 부분을 dispatch 로 변경해 해결했습니다.

아래 코드는 라라벨 5.5 쪽에 작성되어 있는 코드 중 일부 입니다.
https://laravel.com/api/5.5/Illuminate/Events/Dispatcher.html

   /**
     * Flush a set of pushed events.
     *
     * @param  string  $event
     * @return void
     */
    public function flush($event)
    {
        $this->dispatch($event.'_pushed');
    }

    /**
     * Register an event subscriber with the dispatcher.
     *
     * @param  object|string  $subscriber
     * @return void
     */
    public function subscribe($subscriber)
    {
        $subscriber = $this->resolveSubscriber($subscriber);

        $subscriber->subscribe($this);
    }