Upgrade elasticsearch-rest-client to 6.5.2

According to the release notes [1] there are no REST client related
changes. This is just to keep up-to-date with the latest version.

[1] https://www.elastic.co/guide/en/elasticsearch/reference/current/release-notes-6.5.2.html

Change-Id: I0569a12ec96078905bed4996209d826e43fe108b
diff --git a/WORKSPACE b/WORKSPACE
index bc72cec..9f8ad85 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -896,8 +896,8 @@
 # and httpasyncclient as necessary.
 maven_jar(
     name = "elasticsearch-rest-client",
-    artifact = "org.elasticsearch.client:elasticsearch-rest-client:6.5.1",
-    sha1 = "d87892e24ef361b9fff5435246b0f0b8f4561fe8",
+    artifact = "org.elasticsearch.client:elasticsearch-rest-client:6.5.2",
+    sha1 = "6ad0dd15affe56be7dfe638fe317bc5f7456b730",
 )
 
 JACKSON_VERSION = "2.9.7"