router.go
func (r *Router) Host(hosts ...string) *Router {
	c := r.route.clone()
	c.Hosts = hosts
	return r.clone(c)
}
func (r *Router) Host(hosts ...string) *Router {
	c := r.route.clone()
	c.Hosts = hosts
	return r.clone(c)
}
// Host lets you specify the host(s) the route is available for