If you plan to enable mail notifications you must install the Laravel Notification Channels Backport package.
Before you run the migrate command make sure you publish the migrations with:
php artisan vendor:publish --provider="Hazzard\Comments\CommentsServiceProvider" --tag=migrations
You can clone the demo for 5.1 to play around before using the script in your app.
For Laravel 5.1 and 5.2 the broadcast option has been disabled.