Fix `Host` header not being sent
Fix `Host` header not being sent

See: https://github.com/golang/go/issues/7682

Custom headers are set using `headers.Set(..)`.
When it comes to the `Host` header however, this will have no impact
because the request uses the `Host` field from `Request`. If it is
not set, then `URL.Host` will be used.

This commit will make `wuzz` behaviour consistent with cURL.

asciimoo/wuzz