Support PHPUnit 6

tests/Spout/Reader/XLSX/Helper/CellHelperTest.php

@@ -3,11 +3,12 @@
 namespace Box\Spout\Reader\XLSX\Helper;
 
 use Box\Spout\Common\Exception\InvalidArgumentException;
+use PHPUnit\Framework\TestCase;
 
 /**
  * Class CellHelperTest
  */
-class CellHelperTest extends \PHPUnit_Framework_TestCase
+class CellHelperTest extends TestCase
 {
     /**
      * @return array