update tests to reflect changes in phpunit 6.0

test/CommonMarkTest.php

@@ -8,7 +8,7 @@
  * @link http://commonmark.org/ CommonMark
  * @link http://git.io/8WtRvQ JavaScript test runner
  */
-class CommonMarkTest extends PHPUnit_Framework_TestCase
+class CommonMarkTest extends \PHPUnit\Framework\TestCase
 {
     const SPEC_URL = 'https://raw.githubusercontent.com/jgm/stmd/master/spec.txt';
 

test/ParsedownTest.php

@@ -1,6 +1,6 @@
 <?php
 
-class ParsedownTest extends PHPUnit_Framework_TestCase
+class ParsedownTest extends \PHPUnit\Framework\TestCase
 {
     final function __construct($name = null, array $data = array(), $dataName = '')
     {

test/bootstrap.php

@@ -1,3 +1,7 @@
 <?php
 
-include 'Parsedown.php';
+include 'Parsedown.php';
+
+if ( ! class_exists('\PHPUnit\Framework\TestCase') && class_exists('\PHPUnit_Framework_TestCase')) {
+    class_alias('\PHPUnit_Framework_TestCase', '\PHPUnit\Framework\TestCase');
+}