Bump elasticsearch in /integration/elasticsearch-jetty

Bumps [elasticsearch](https://github.com/elastic/elasticsearch) from 1.5.2 to 6.8.13.
- [Release notes](https://github.com/elastic/elasticsearch/releases)
- [Commits](https://github.com/elastic/elasticsearch/compare/v1.5.2...v6.8.13)
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integration/elasticsearch-jetty/pom.xml

@@ -10,7 +10,7 @@
   <packaging>jar</packaging>
 
   <properties>
-    <elasticsearch.version>1.5.2</elasticsearch.version>
+    <elasticsearch.version>6.8.13</elasticsearch.version>
     <jetty.version>9.4.35.v20201120</jetty.version>
   </properties>