def update_devices(devices)
      devices= [devices] unless devices.kind_of?(Array)

      # the list of ANDROID push_id to send the notification to
      @andr_ids= []
      @ios_devices= []
      devices.each do |device|
        if Platforms.android? device.platform
          @andr_ids << device.push_id
        elsif Platforms.ios? device.platform
          @ios_devices << device
        end
      end
      self
    end
def update_devices(devices)
      devices= [devices] unless devices.kind_of?(Array)

      # the list of ANDROID push_id to send the notification to
      @andr_ids= []
      @ios_devices= []
      devices.each do |device|
        if Platforms.android? device.platform
          @andr_ids << device.push_id
        elsif Platforms.ios? device.platform
          @ios_devices << device
        end
      end
      self
    end
+credentials+ is a hash with 2 keys :andr and :ios, each one with its
 given credentials:
 - :andr => a string with the notification_key
 - :ios  => a hash of the form {
    host: 'test-host',
    pem: 'test-pem',
    port: 'test-port',
    pass: 'test-password',
  }