Bump gson from 2.8.1 to 2.8.9 in /promql_client

Bumps [gson](https://github.com/google/gson) from 2.8.1 to 2.8.9.
- [Release notes](https://github.com/google/gson/releases)
- [Changelog](https://github.com/google/gson/blob/master/CHANGELOG.md)
- [Commits](https://github.com/google/gson/compare/gson-parent-2.8.1...gson-parent-2.8.9)

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

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

promql_client/pom.xml

@@ -24,7 +24,7 @@
 		<dependency>
 			<groupId>com.google.code.gson</groupId>
 			<artifactId>gson</artifactId>
-			<version>2.8.1</version>
+			<version>2.8.9</version>
 		</dependency>
 	</dependencies>
 </project>