deps: update dependency com.google.code.gson:gson to v2.8.9 (googleapis#509)

Author: renovate-bot

third-party-dependencies/pom.xml

@@ -57,7 +57,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <site.installationModule>${project.artifactId}</site.installationModule>
 
-    <gson.version>2.8.8</gson.version>
+    <gson.version>2.8.9</gson.version>
     <threeten.version>1.5.1</threeten.version>
     <javax.annotations.version>1.3.2</javax.annotations.version>
     <animal-sniffer.version>1.20</animal-sniffer.version>