Add Laravel 5.8 support

tests/TestCase.php

@@ -9,7 +9,7 @@ use BeyondCode\Comments\CommentsServiceProvider;
 abstract class TestCase extends \Orchestra\Testbench\TestCase
 {
 
-    public function setUp()
+    public function setUp(): void
     {
         parent::setUp();
         $this->loadLaravelMigrations(['--database' => 'sqlite']);