elk: 5.4.2 -> 5.5.2

Release notes:

* https://www.elastic.co/guide/en/elasticsearch/reference/5.5/release-notes-5.5.2.html
* https://www.elastic.co/guide/en/logstash/5.5/logstash-5-5-2.html
* https://www.elastic.co/guide/en/kibana/current/release-notes-5.5.2.html