Bump jackson2.version from 2.8.6 to 2.10.2 in /guestbook

Bumps `jackson2.version` from 2.8.6 to 2.10.2.

Updates `jackson-databind` from 2.8.6 to 2.10.2
- [Release notes](https://github.com/FasterXML/jackson/releases)
- [Commits](https://github.com/FasterXML/jackson/commits)

Updates `jackson-datatype-jdk8` from 2.8.6 to 2.10.2

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

guestbook/pom.xml

@@ -10,7 +10,7 @@
   <properties>
   	<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   	<spring.version>4.3.5.RELEASE</spring.version>
-  	<jackson2.version>2.8.6</jackson2.version>
+  	<jackson2.version>2.10.2</jackson2.version>
   </properties>
 
   <dependencies>