Use PHP-5.3 compliant syntax

Author: erayd

src/JsonSchema/Constraints/FormatConstraint.php

@@ -89,8 +89,8 @@ public function check(&$element, $schema = null, JsonPointer $path = null, $i =
                     } elseif (substr($element, 0, 1) === '/') { // absolute-path reference
                         $validURL = filter_var('scheme://host' . $element, FILTER_VALIDATE_URL, FILTER_NULL_ON_FAILURE);
                     } elseif (strlen($element)) { // relative-path reference
-                        $pathParts = explode('/', $element, 2)[0];
-                        if ($pathParts[0] !== '.' && strpos($pathParts, ':') !== false) {
+                        $pathParts = explode('/', $element, 2);
+                        if ($pathParts[0][0] !== '.' && strpos($pathParts[0], ':') !== false) {
                             $validURL = null;
                         } else {
                             $validURL = filter_var('scheme://host/' . $element, FILTER_VALIDATE_URL, FILTER_NULL_ON_FAILURE);