FIX RSS feed for comments now render correctly

The comment DataList filter applies ParentClass = $className - when this
is the base class, it fails to recognise comments for a BlogPost. This
change uses the late class name instead.

src/Extensions/CommentsExtension.php

@@ -441,7 +441,7 @@ class CommentsExtension extends DataExtension
     {
         return Controller::join_links(
             $this->getCommentRSSLink(),
-            str_replace('\\', '-', $this->owner->baseClass()),
+            str_replace('\\', '-', get_class($this->owner)),
             $this->owner->ID
         );
     }