Move broadcast channel registration to a routes file.

These are very similar to routes in that they are channel endpoints
that your application supports and they also fully support route model
binding in Laravel 5.4. Upgraded applications do not need to make this
change if they do not want to.

config/app.php

@@ -196,6 +196,7 @@ return [
         'Artisan' => Illuminate\Support\Facades\Artisan::class,
         'Auth' => Illuminate\Support\Facades\Auth::class,
         'Blade' => Illuminate\Support\Facades\Blade::class,
+        'Broadcast' => Illuminate\Support\Facades\Broadcast::class,
         'Bus' => Illuminate\Support\Facades\Bus::class,
         'Cache' => Illuminate\Support\Facades\Cache::class,
         'Config' => Illuminate\Support\Facades\Config::class,