Please clarify support for Elasticsearch 5.6 in the documentation

The Elasticsearch integration document lists Elasticsearch versions 5.1 through 5.5 as supported, and 6.0 and above as unsupported. The support status for the version 5.6, which is currently the latest in the 5.x family, is thus left undefined.

Please update the document to explicitly confirm or deny support for Elasticsearch 5.6.x.