Bump gson from 2.2.4 to 2.8.9

Bumps [gson](https://github.com/google/gson) from 2.2.4 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-2.2.4...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>
diff --git a/pom.xml b/pom.xml
index 58f1375..a109448 100644
--- a/pom.xml
+++ b/pom.xml
@@ -204,7 +204,7 @@
     <!-- Dependencies versions -->
     <fastutil.version>6.5.6</fastutil.version>
     <findbugs.jsr305.version>2.0.1</findbugs.jsr305.version>
-    <gson.version>2.2.4</gson.version>
+    <gson.version>2.8.9</gson.version>
     <guava.version>13.0.1</guava.version>
     <guice.version>3.0</guice.version>
     <logback.version>1.2.3</logback.version>