Fixed string access by curly brace to bracket

This seems to be the version officially favored by PHP:
http://www.php.net/manual/en/language.types.string.php#language.types.string.substr

src/Symfony/Component/Validator/ConstraintViolationList.php

@@ -50,7 +50,7 @@ class ConstraintViolationList implements \IteratorAggregate, \Countable, \ArrayA
             $root = $violation->getRoot();
             $class = (string) (is_object($root) ? get_class($root) : $root);
             $propertyPath = (string) $violation->getPropertyPath();
-            if ('' !== $propertyPath && '[' !== $propertyPath{0} && '' !== $class) {
+            if ('' !== $propertyPath && '[' !== $propertyPath[0] && '' !== $class) {
                 $class .= '.';
             }
             $string .= <<<EOF