Update dependency org.apache.maven.plugins:maven-jar-plugin to v2.6

Author: renovate[bot]

pom.xml

@@ -29,7 +29,7 @@
     <plugin.version.clean>2.6.1</plugin.version.clean>
     <plugin.version.source>3.3.1</plugin.version.source>
     <plugin.version.compiler>3.14.0</plugin.version.compiler>
-    <plugin.version.jar>2.5</plugin.version.jar>
+    <plugin.version.jar>2.6</plugin.version.jar>
     <plugin.version.javadoc>3.10.0</plugin.version.javadoc>
     <plugin.version.maven-bundle>5.1.9</plugin.version.maven-bundle>