Update dependency com.google.code.gson:gson to v2.8.9 (#62)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

build.gradle

@@ -183,7 +183,7 @@ repositories {
 }
 
 ext {
-  gsonVersion = "2.8.8"
+  gsonVersion = "2.8.9"
   commonsValidatorVersion = "1.7"
   jsonVersion = "20210307"
   junitVersion = "4.13.2"