def listen(*events)
      events.each do |event|
        EVENTS.include?(event) or
          raise ArgumentError, "invalid event: #{event.inspect}"
      end
      @actor << [ "LISTEN", *events ]
    end
def listen(*events)
      events.each do |event|
        EVENTS.include?(event) or
          raise ArgumentError, "invalid event: #{event.inspect}"
      end
      @actor << [ "LISTEN", *events ]
    end
Configure monitor to listen for specific events.
 @param events [String] one or more events from {EVENTS}
 @return [void]