[MNGSITE-214] Different versions of the Site Descriptor XSD are referenced (1.3.0 and 1.4.0)

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1647424 13f79535-47bb-0310-9956-ffa450edef68
Update Site Decorator version to 1.6.0 in site.xml because we are using 1.6 of Doxia Sitetools

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1647430 13f79535-47bb-0310-9956-ffa450edef68