Fix the issue on missing/exceeding 'www.'

in some host/wordpress configurations that falls in a 'Domains, protocols and ports must match' error.

If a domain is set to work with the www (i.e.: www.domain.com), if i call it without the www, it'll be placed automagically. But if i call the sitemap without the www it's loaded without the www, and the stylesheet is unreachable because of the reported bug.

That's the fixment.