Bump elasticsearch in /hippo4j-monitor/hippo4j-monitor-es

Bumps [elasticsearch](https://github.com/elastic/elasticsearch) from 6.5.0 to 6.8.17.
- [Release notes](https://github.com/elastic/elasticsearch/releases)
- [Changelog](https://github.com/elastic/elasticsearch/blob/main/CHANGELOG.md)
- [Commits](https://github.com/elastic/elasticsearch/compare/v6.5.0...v6.8.17)

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

Signed-off-by: dependabot[bot] <support@github.com>

hippo4j-monitor/hippo4j-monitor-es/pom.xml

@@ -10,7 +10,7 @@
     <artifactId>hippo4j-monitor-es</artifactId>
 
     <properties>
-        <elasticsearch.version>6.5.0</elasticsearch.version>
+        <elasticsearch.version>6.8.17</elasticsearch.version>
     </properties>
 
     <dependencies>