Add support for ES 7.6.0

Author: ejsmith

build/docker/elasticsearch/Dockerfile

@@ -1,5 +1,5 @@
 # https://www.docker.elastic.co/
-FROM docker.elastic.co/elasticsearch/elasticsearch:7.5.2
+FROM docker.elastic.co/elasticsearch/elasticsearch:7.6.0
 
 RUN elasticsearch-plugin install -b mapper-size
 RUN elasticsearch-plugin install -b repository-azure