Add 3.13 to plugin-manager

Change-Id: Ic04f6d42e61dbc4d788884c99abaa8e36615697b
diff --git a/jenkins-docker/server/plugin-manager/index.html b/jenkins-docker/server/plugin-manager/index.html
index 5b45e25..7fc6602 100644
--- a/jenkins-docker/server/plugin-manager/index.html
+++ b/jenkins-docker/server/plugin-manager/index.html
@@ -29,6 +29,7 @@
                   <option value="stable-3.10">v3.10.x</option>
                   <option value="stable-3.11">v3.11.x</option>
                   <option value="stable-3.12">v3.12.x</option>
+                  <option value="stable-3.13">v3.13.x</option>
                   <option value="master">master</option>
                 </select>
                 <input type="text" class="form-control searchbox" placeholder="Search" ng-model="searchPlugin">