Fix return type hint

src/HAB/Solr/Facet/Value/Container/FacetValueTree.php

@@ -82,7 +82,7 @@ class FacetValueTree implements ContainerInterface
     /**
      * Return the root node.
      *
-     * @return Node
+     * @return FacetValueTreeNode
      */
     public function getRootNode ()
     {
@@ -214,4 +214,4 @@ class FacetValueTree implements ContainerInterface
         $this->rootNode->sortByValueFunction($sortfunc, $reverse);
     }
 
-}
\ No newline at end of file
+}