Bump elasticsearch from 5.6.5 to 6.8.17

Bumps [elasticsearch](https://github.com/elastic/elasticsearch) from 5.6.5 to 6.8.17.
- [Release notes](https://github.com/elastic/elasticsearch/releases)
- [Commits](elastic/elasticsearch@v5.6.5...v6.8.17)

---
updated-dependencies:
- dependency-name: org.elasticsearch:elasticsearch
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

pom.xml

@@ -19,7 +19,7 @@
     </licenses>
 
     <properties>
-        <elasticsearch.version>5.6.5</elasticsearch.version>
+        <elasticsearch.version>6.8.17</elasticsearch.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <skipTests>false</skipTests>
         <skipUnitTests>${skipTests}</skipUnitTests>