fix(phpunit) Make TestCase abstract.

Author: Hywan

phpunit/TestCase.php

@@ -1,13 +1,13 @@
 <?php
 
 namespace PHPUnit\Framework {
-    class TestCase extends \mageekguy\atoum\phpunit\test
+    abstract class TestCase extends \mageekguy\atoum\phpunit\test
     {
     }
 }
 
 namespace {
-    class PHPUnit_Framework_TestCase extends \PHPUnit\Framework\TestCase
+    abstract class PHPUnit_Framework_TestCase extends \PHPUnit\Framework\TestCase
     {
     }
 }