Upgrade to Gson 2.6.1

Closes gh-5236

spring-boot-dependencies/pom.xml

@@ -71,7 +71,7 @@
 		<glassfish-el.version>3.0.0</glassfish-el.version>
 		<gradle.version>1.12</gradle.version>
 		<groovy.version>2.4.6</groovy.version>
-		<gson.version>2.5</gson.version>
+		<gson.version>2.6.1</gson.version>
 		<h2.version>1.4.191</h2.version>
 		<hamcrest.version>1.3</hamcrest.version>
 		<hazelcast.version>3.5.5</hazelcast.version>