Upgrade to Gson 2.8.4

Closes gh-13054

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -79,7 +79,7 @@
 		<glassfish-el.version>3.0.0</glassfish-el.version>
 		<gradle.version>2.9</gradle.version>
 		<groovy.version>2.4.15</groovy.version>
-		<gson.version>2.8.2</gson.version>
+		<gson.version>2.8.4</gson.version>
 		<h2.version>1.4.197</h2.version>
 		<hamcrest.version>1.3</hamcrest.version>
 		<hazelcast.version>3.7.8</hazelcast.version>