Bump gson from 2.2 to 2.8.9 in /shell (#4381)

Bumps [gson](https://github.com/google/gson) from 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](https://github.com/google/gson/compare/gson-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] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
diff --git a/shell/pom.xml b/shell/pom.xml
index 29c5639..dbc048b 100644
--- a/shell/pom.xml
+++ b/shell/pom.xml
@@ -38,7 +38,7 @@
     <pty4j.version>0.9.3</pty4j.version>
     <jinjava.version>2.4.0</jinjava.version>
     <guava.version>24.1.1-jre</guava.version>
-    <gson.version>2.2</gson.version>
+    <gson.version>2.8.9</gson.version>
   </properties>
 
   <!-- pty4j library not in maven central repository (http://repo.maven.apache.org/maven2) -->