public PayloadBuilder instantDeliveryOrSilentNotification() {
        aps.put("content-available", 1);
        return this;
    }
With iOS7 it is possible to have the application wake up before the user opens the app.

The same key-word can also be used to send 'silent' notifications. With these 'silent' notification 
a different app delegate is being invoked, allowing the app to perform background tasks.

@return this
src/main/java/com/notnoop/apns/PayloadBuilder.java