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](apache/maven-jar-plugin@maven-jar-plugin-2.6...maven-jar-plugin-3.1.2)

pom.xml

@@ -74,7 +74,7 @@
         <bintray.package>kernel</bintray.package>
 
         <buildnumber-maven-plugin.version>1.4</buildnumber-maven-plugin.version>
-        <maven-jar-plugin.version>2.6</maven-jar-plugin.version>
+        <maven-jar-plugin.version>3.1.2</maven-jar-plugin.version>
 
     </properties>