Where all first level keys corresponds to an service configuration, each service has its own properties, android for instance have apiKey and IOS uses certificate and passPhrase. You can set as many services configurations as you want, one for each app. A directory with the name 'ios-push-notification-certificates' will be added to the config folder for you to store both development and production certificates.
Dont forget to set service key to identify iOS 'service'=>'apns' and Android 'service'=>'gcm'
PushNotification::app('iOS')->to($deviceToken)->send('Hello World, i`m a push message');