Maven 3.1 requires maven-dependency-plugin 2.8

After upgrading to Maven 3.1.1 I can not execute mvm dependency:tree which is caused the migration from Sonatype Aether to Eclipse Aether (MNG-5354)

This is fixed by upgrading the maven dependency plugin to v2.8

Note: The following page contains all plugins that are affected by this change https://cwiki.apache.org/confluence/display/MAVEN/AetherClassNotFound