Reduce severity of logged warning about document _type

[wallrik]

There's a warning that triggers every time I start Logstash that feels very outdated:

logstash-output-elasticsearch/lib/logstash/outputs/elasticsearch/http_client/pool.rb

Lines 496 to 498 in 48ddb89

	if major >= 6
	@logger.warn("Detected a 6.x and above cluster: the `type` event field won't be used to determine the document _type", es_version: major)
	end

Is there any chance that line can be changed to debug level for the next version of this plugin? Or, maybe info level and only trigger on major version 6 or 7?