Update ExampleTest.

Author: irazasyed

tests/ExampleTest.php

@@ -2,12 +2,12 @@
 
 namespace NotificationChannels\Facebook\Test;
 
-use PHPUnit_Framework_TestCase;
+use PHPUnit\Framework\TestCase;
 
 /**
  * Class ExampleTest.
  */
-class ExampleTest extends PHPUnit_Framework_TestCase
+class ExampleTest extends TestCase
 {
     /** @test */
     public function true_is_true(): void