[maven-release-plugin] prepare release maven-dependency-tree-2.1

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1478610 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1478612 13f79535-47bb-0310-9956-ffa450edef68