Added fix for isURL validator, when protocol is followed by a www

[GEMI]

Hey, hope you can merge this is, because we have issues in our app with incorrect URL's. Thanks!

[chriso]

Sorry, I can't merge this; this is not correct. There's nothing special about www. versus any other subdomain. For example, http://www.com/ is a valid URL, resolves correctly and is a real parked website (try it!).

The example you gave in #428 is a valid URL, but the .uk TLD seem to have disallowed registration of that domain. Checking this is outside the scope of the library. If you need extra validation, I'd suggest you try looking up the DNS entry (A) to see if the domain resolves, and then possibly visiting the site to see if it exists or not. If I visit http://www.uk I get redirected to a http://error.talktalk.co.uk page telling me that the domain does not exist. The fact that visiting http://www.uk in the browser takes me to a real page is more proof that it's a valid URL 😉