Bump gson from 2.8.5 to 2.8.9

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](https://github.com/google/gson/compare/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] <support@github.com>

pom.xml

@@ -18,7 +18,7 @@
     <maven.compiler.target>1.8</maven.compiler.target>
 
     <spark.version>2.7.2</spark.version>
-    <gson.version>2.8.5</gson.version>
+    <gson.version>2.8.9</gson.version>
   </properties>
 
   <dependencies>