Bump maven-jar-plugin from 2.6 to 3.1.2
Bump maven-jar-plugin from 2.6 to 3.1.2

Bumps [maven-jar-plugin](https://github.com/apache/maven-jar-plugin) from 2.6 to 3.1.2.
- [Release notes](https://github.com/apache/maven-jar-plugin/releases)
- [Commits](https://github.com/apache/maven-jar-plugin/compare/maven-jar-plugin-2.6...maven-jar-plugin-3.1.2)
gturri/aXMLRPC,gturri/aXMLRPC,timroes/aXMLRPC