[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1621735 13f79535-47bb-0310-9956-ffa450edef68
Reverted update to released versions not available on Maven Central

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1621736 13f79535-47bb-0310-9956-ffa450edef68