Upgrade elasticsearch-rest-client to 6.5.3

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

[1] https://www.elastic.co/guide/en/elasticsearch/reference/current/release-notes-6.5.3.html

Change-Id: I2878451d9e6f146e83779a3b639346828b50b0ca
diff --git a/WORKSPACE b/WORKSPACE
index 9f8ad85..fc5de68 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:6.5.2",
-    sha1 = "6ad0dd15affe56be7dfe638fe317bc5f7456b730",
+    artifact = "org.elasticsearch.client:elasticsearch-rest-client:6.5.3",
+    sha1 = "ac8df46fce1c01b61cbf1f84186bf910d12b577e",
 )
 
 JACKSON_VERSION = "2.9.7"