Typo fixed

Author: Ph3nol

doc/apns-adapter.md

@@ -124,7 +124,7 @@ use Sly\NotificationPusher\PushManager,
 // First, instantiate the manager.
 //
 // Example for production environment:
-// $pushManager = new PushManager(PushManager::ENVIRONMENT_PRODUCTION);
+// $pushManager = new PushManager(PushManager::ENVIRONMENT_PROD);
 //
 // Development one by default (without argument).
 $pushManager = new PushManager(PushManager::ENVIRONMENT_DEV);