update version of elastic and kibana (#1996)

elasticsearch/Dockerfile

@@ -1,3 +1,3 @@
-FROM docker.elastic.co/elasticsearch/elasticsearch:6.2.3
+FROM docker.elastic.co/elasticsearch/elasticsearch:6.6.0
 
 EXPOSE 9200 9300

kibana/Dockerfile

@@ -1,3 +1,3 @@
-FROM docker.elastic.co/kibana/kibana:6.2.3
+FROM docker.elastic.co/kibana/kibana:6.6.0
 
 EXPOSE 5601