Use RFC 2606 reserved invalid DNS name in tests.

This test used a DNS name which, while currently not existing, is not
actually reserved. This can manifest as a test failure on poorly
configured (like Time Warner Cable) networks. This changes said DNS
name to one using a reserved invalid top level name as specified in
RFC 2606.

test/test_bad_schema_ref.rb

@@ -29,7 +29,7 @@ def test_bad_host_ref
     schema = {
       "$schema" => "http://json-schema.org/draft-04/schema#",
       "type" => "array",
-      "items" => { "$ref" => "http://ppcheesecheseunicornnuuuurrrrr.com/json.schema"}
+      "items" => { "$ref" => "http://ppcheesecheseunicornnuuuurrrrr.example.invalid/json.schema"}
     }
 
     data = [1,2,3]