deps: update dependency com.google.code.gson:gson to v2.8.8 (#442)

Author: renovate-bot

pom.xml

@@ -66,7 +66,7 @@
     <google.http-client.version>1.39.2</google.http-client.version>
     <google.oauth-client.version>1.31.5</google.oauth-client.version>
     <google.api-client.version>1.32.1</google.api-client.version>
-    <gson.version>2.8.7</gson.version>
+    <gson.version>2.8.8</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>