Bump gson from 2.8.7 to 2.8.9

Bumps [gson](https://github.com/google/gson) from 2.8.7 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-2.8.7...gson-parent-2.8.9)

---
updated-dependencies:
- dependency-name: com.google.code.gson:gson
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

build.gradle

@@ -65,7 +65,7 @@ dependencies {
   compile group: 'cd.go.plugin.base', name: 'gocd-plugin-base', version: '0.0.1'
   compileOnly group: 'cd.go.plugin', name: 'go-plugin-api', version: '21.2.0'
   compile group: 'com.bettercloud', name: 'vault-java-driver', version: '5.1.0'
-  compile group: 'com.google.code.gson', name: 'gson', version: '2.8.7'
+  compile group: 'com.google.code.gson', name: 'gson', version: '2.8.9'
 
   testCompile group: 'org.junit.jupiter', name: 'junit-jupiter-engine', version: '5.7.2'
   testCompile group: 'org.junit.jupiter', name: 'junit-jupiter-api', version: '5.7.2'