Bump gson from 2.8.1 to 2.8.9

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>
diff --git a/pom.xml b/pom.xml
index de30e11..93ccd07 100644
--- a/pom.xml
+++ b/pom.xml
@@ -94,7 +94,7 @@
         <gmaven.version>1.3</gmaven.version> <!-- Newest: 1.5 -->
 
         <guava.version>14.0.1</guava.version> <!-- Newest: 18.0 -->
-        <gson.version>2.8.1</gson.version>
+        <gson.version>2.8.9</gson.version>
 
         <httpcomponents.httpclient.version>4.5.2</httpcomponents.httpclient.version> <!-- Newest: 4.5.3 -->
         <httpcomponents.httpcore.version>4.4.4</httpcomponents.httpcore.version> <!-- Newest: 4.4.6 -->