Elasticsearch 5: Close content builder

This commit wraps the usage of a content builder in a try-with-resources
block to ensure that it is correctly closed.

elasticsearch5/src/main/java/com/yahoo/ycsb/db/elasticsearch5/ElasticsearchClient.java

@@ -150,8 +150,7 @@ public class ElasticsearchClient extends DB {
 
   @Override
   public Status insert(String table, String key, Map<String, ByteIterator> values) {
-    try {
-      final XContentBuilder doc = jsonBuilder();
+    try (XContentBuilder doc = jsonBuilder()) {
 
       doc.startObject();
       for (final Entry<String, String> entry : StringByteIterator.getStringMap(values).entrySet()) {