ElasticContainer: Use Elasticsearch 5.6.12 for V5_6 tests

Change-Id: Icb85272a3c1d68700d7b251d643c8640a82adfb7
diff --git a/gerrit-elasticsearch/src/main/java/com/google/gerrit/elasticsearch/testing/ElasticContainer.java b/gerrit-elasticsearch/src/main/java/com/google/gerrit/elasticsearch/testing/ElasticContainer.java
index b20afca..4e95674 100644
--- a/gerrit-elasticsearch/src/main/java/com/google/gerrit/elasticsearch/testing/ElasticContainer.java
+++ b/gerrit-elasticsearch/src/main/java/com/google/gerrit/elasticsearch/testing/ElasticContainer.java
@@ -46,7 +46,7 @@
       case V2_4:
         return "elasticsearch:2.4.6-alpine";
       case V5_6:
-        return "docker.elastic.co/elasticsearch/elasticsearch:5.6.11";
+        return "docker.elastic.co/elasticsearch/elasticsearch:5.6.12";
       case V6_2:
         return "docker.elastic.co/elasticsearch/elasticsearch-oss:6.2.4";
       case V6_3: