Added docbloc to UniqueTokenIdentifierConstraintViolationException

src/Exception/UniqueTokenIdentifierConstraintViolationException.php

@@ -11,6 +11,9 @@ namespace League\OAuth2\Server\Exception;
 
 class UniqueTokenIdentifierConstraintViolationException extends OAuthServerException
 {
+    /**
+     * @return UniqueTokenIdentifierConstraintViolationException
+     */
     public static function create()
     {
         $errorMessage = 'Could not create unique access token identifier';