Skip the Factory specs for sebastian/comparator 5+

This deprecated class is not compatible with the new major version of
sebastian/comparator.

spec/Prophecy/Comparator/FactorySpec.php

@@ -2,11 +2,23 @@
 
 namespace spec\Prophecy\Comparator;
 
+use PhpSpec\Exception\Example\SkippingException;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
+use Prophecy\Comparator\Factory;
+use SebastianBergmann\Comparator\Factory as BaseFactory;
 
 class FactorySpec extends ObjectBehavior
 {
+    function let()
+    {
+        $ref = new \ReflectionClass(BaseFactory::class);
+
+        if ($ref->isFinal()) {
+            throw new SkippingException(sprintf('The deprecated "%s" class cannot be used with sebastian/comparator 5+.', Factory::class));
+        }
+    }
+
     function it_extends_Sebastian_Comparator_Factory()
     {
         $this->shouldHaveType('SebastianBergmann\Comparator\Factory');