minor symfony#15851 Fix the phpdoc in the CssSelector TranslatorInterface (stof)

This PR was merged into the 2.3 branch.

Discussion
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Fix the phpdoc in the CssSelector TranslatorInterface

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

The phpdoc of the interface does not match the behavior of the implementation. And the return type documented by the interface is impossible to return because the interface asks to apply a string prefix, and the only way is to cast the ``XPathExpr`` used internally to a string (which is what the implementation does).

This interface is an internal interface anyway.

Commits
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93ffa61 Fix the phpdoc in the CssSelector TranslatorInterface

Author: fabpot

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