missing constraint parameter in url

[poolerMF]

http://symfony.com/doc/current/reference/constraints/Url.html

-> missing parameter dnsMessage

[xabbuh]

Thank you for reporting this @poolerMF.

For anyone wanting to work on this: Changes should be applied on the 2.7 branch. The dnsMessage option was introduced in symfony/symfony#12956 together with the checkDns option and controls the message that will be shown in case the DNS check failed.