Elasticsearch version checking for version 5.1-5.5 in 11.5.4

The Elasticseach version check in the app check rake task is checking for version 5.1-5.4 instead of 5.6-6.x as highlighted in doc/integration/elasticsearch.md. As such an installation with the required version of Elastic search fails this check.

Screen_Shot_2018-12-19_at_11.37.57

The file responsile for the Elasticsearch version check seems to have been updated accordingly.