Fixed minor typo to variable name in Extension example

git-svn-id: http://framework.zend.com/svn/framework/standard/trunk@16968 44c647ce-9c0f-0410-b52a-842ac1e357ba

documentation/manual/en/module_specs/Zend_Feed_Reader.xml

@@ -1271,7 +1271,7 @@ class My_FeedReader_Extension_JungleBooks_Entry
         if (!$isbn) {
             $isbn = null;
         }
-        $this->_data['isbn'] = $title;
+        $this->_data['isbn'] = $isbn;
         return $this->_data['isbn'];
     }