Merge branch 'stable-2.15'

* stable-2.15:
  ElasticContainer: Use Elasticsearch 6.4.2 for V6_4 tests
  Upgrade elasticsearch-rest-client to 6.4.2

Change-Id: Ice17dc2ce03418d75333a489522c53f376d1a657
diff --git a/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java b/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java
index f67f990..bb545c9 100644
--- a/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java
+++ b/javatests/com/google/gerrit/elasticsearch/ElasticContainer.java
@@ -51,7 +51,7 @@
       case V6_3:
         return "docker.elastic.co/elasticsearch/elasticsearch-oss:6.3.2";
       case V6_4:
-        return "docker.elastic.co/elasticsearch/elasticsearch-oss:6.4.1";
+        return "docker.elastic.co/elasticsearch/elasticsearch-oss:6.4.2";
     }
     throw new IllegalStateException("No tests for version: " + version.name());
   }