fix Class/Sitemap.php : mkdir doesn't return $this

library/Class/Sitemap.php

@@ -110,8 +110,8 @@ class Class_Sitemap {
 
     $this->xml->appendChild($urlset);
 
-    $this->file_system->mkdir(PATH_TEMP)
-                      ->filePutContents(static::getSitemapPath(),
+    $this->file_system->mkdir(PATH_TEMP);
+    $this->file_system->filePutContents(static::getSitemapPath(),
                                         $this->xml->saveXML());
     return $this;
   }