Bump gson from 2.2.2 to 2.8.9 in /wicket-pivot

Bumps [gson](https://github.com/google/gson) from 2.2.2 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-2.2.2...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]

wicket-pivot/pom.xml

@@ -15,7 +15,7 @@
 	<description>Simple web pivot table using Apache Wicket</description>
 
 	<properties>
-        <gson.version>2.2.2</gson.version>
+        <gson.version>2.8.9</gson.version>
 	</properties>
 
 	<dependencies>