Add missing license headers.

git-svn-id: https://svn.apache.org/repos/asf/maven/plugin-tools/trunk@1585579 13f79535-47bb-0310-9956-ffa450edef68
Add missing license header.

git-svn-id: https://svn.apache.org/repos/asf/maven/plugin-tools/trunk@1585580 13f79535-47bb-0310-9956-ffa450edef68