knotserver: have top level router use cors header function

Signed-off-by: @nekomimi.pet <[e-mail]>

knotserver/router.go

···
 func (h *Knot) Router() http.Handler {
 	r := chi.NewRouter()
 
+	r.Use(h.CORS)
 	r.Use(h.RequestLogger)
 
 	r.Get("/", func(w http.ResponseWriter, r *http.Request) {