Fix the phpdoc in the CssSelector TranslatorInterface

src/Symfony/Component/CssSelector/XPath/TranslatorInterface.php

@@ -29,7 +29,7 @@ interface TranslatorInterface
      * @param string $cssExpr
      * @param string $prefix
      *
-     * @return XPathExpr
+     * @return string
      */
     public function cssToXPath($cssExpr, $prefix = 'descendant-or-self::');
 
@@ -39,7 +39,7 @@ interface TranslatorInterface
      * @param SelectorNode $selector
      * @param string       $prefix
      *
-     * @return XPathExpr
+     * @return string
      */
     public function selectorToXPath(SelectorNode $selector, $prefix = 'descendant-or-self::');
 }