Upgrade Elasticsearch to 2.4.4

Version 2.4.4 is the latest on the 2.4.x series, and still uses
Lucene 5.5.2 which is the version used in Gerrit.

Change-Id: I30d9ebeb8532131fc8abd646447006af30156777
diff --git a/WORKSPACE b/WORKSPACE
index fe578fc..6d9baed 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -906,8 +906,8 @@
 
 maven_jar(
     name = "elasticsearch",
-    artifact = "org.elasticsearch:elasticsearch:2.4.0",
-    sha1 = "aeb9704a76fa8654c348f38fcbb993a952a7ab07",
+    artifact = "org.elasticsearch:elasticsearch:2.4.4",
+    sha1 = "e69930bc794c539d34778e665d6f8ccbffd42c6f",
 )
 
 # Java REST client for Elasticsearch.