Readd placeholder for site generation

Does not yet work properly, just added as a reminder.


git-svn-id: https://svn.apache.org/repos/asf/creadur/rat/trunk@1845845 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index cf654da..5496e7b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -74,6 +74,7 @@
     <!-- maven plugin versions -->
     <mavenPluginPluginVersion>3.3</mavenPluginPluginVersion>
     <mavenChangesVersion>2.11</mavenChangesVersion>
+    <previousRatVersion>0.12</previousRatVersion>
   </properties>
   <dependencyManagement>
     <dependencies>