chore(deps): bump gson from 2.8.6 to 2.8.9 in /tools/api-generator (#937)

Author: dependabot[bot]

tools/api-generator/pom.xml

@@ -14,7 +14,7 @@
   </description>
   <properties>
     <compiler.version>1.8</compiler.version>
-    <gson.version>2.8.6</gson.version>
+    <gson.version>2.8.9</gson.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>