Documentation for metrics filter uses wrong example

The documentation for the metrics filter gives an example:

...
output {

1. only emit events with the 'metric' tag
   if "metric" in [tags] {
   stdout
   Unknown macro: { message => "rate}

   }
   }

However 'message' is a deprecated field of stdout. According to https://logstash.jira.com/browse/LOGSTASH-1413, this should be changed to use the line output.