Added the missing class import

Author: javiereguiluz

components/phpunit_bridge.rst

@@ -551,6 +551,7 @@ the data you expect to get for the given hosts::
 
     use App\Validator\DomainValidator;
     use PHPUnit\Framework\TestCase;
+    use Symfony\Bridge\PhpUnit\DnsMock;
 
     /**
      * @group dns-sensitive