Bump gson in /cf-java-monitoring-custom-metrics-clients

Bumps [gson](https://github.com/google/gson) from 2.8.5 to 2.8.9.
- [Release notes](https://github.com/google/gson/releases)
- [Changelog](https://github.com/google/gson/blob/master/CHANGELOG.md)
- [Commits](google/gson@gson-parent-2.8.5...gson-parent-2.8.9)

---
updated-dependencies:
- dependency-name: com.google.code.gson:gson
  dependency-type: direct:production
...

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

Author: dependabot[bot]

cf-java-monitoring-custom-metrics-clients/pom.xml

@@ -27,7 +27,7 @@
             <dependency>
                 <groupId>com.google.code.gson</groupId>
                 <artifactId>gson</artifactId>
-                <version>2.8.5</version>
+                <version>2.8.9</version>
             </dependency>
             <dependency>
                 <groupId>org.slf4j</groupId>