Class 'App\Exceptions\Handler' not found

@tiran133 reported the following commit breaks his app: https://github.com/rollbar/rollbar-php-laravel/commit/b9ce5ef82d0d8664063a6ebb6c1143730b86b26a#commitcomment-30114382

Assuming `App\Exceptions\Handler` exists in user's app is too much of a stretch. We need a different solution for registering an automatic exception handler.