I am thinking probably the validation itself is not required since the validation kicks in only on user entering the value. The URL itself can be left blank since it is not required field unlike email or name.
Can you set the line number 311 to 314 of js/main.js to –
and see if that helps? Hope this meets your needs.
Im having the same issue with the default contact form. ! how can modify the default contact list or remove the opcion WEB URL for something else or an easy way to user add their website without http:// – it tells the user that it’s not a valid url when http:// is missing.