Document test plugin requirement

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@393395 13f79535-47bb-0310-9956-ffa450edef68

jar/xdocs/index.xml

@@ -45,6 +45,7 @@
       <ul>
         <li>maven-plugin-plugin 1.7 (at least)</li>
         <li>maven-artifact-plugin 1.3 (at least)</li>
+        <li>maven-test-plugin 1.8 (at least)</li>
       </ul>
     </section>
  </body>