fix: fix static assets url generation (#965)

http/utils.go

@@ -43,7 +43,7 @@ func errToStatus(err error) int {
 // This is an addaptation if http.StripPrefix in which we don't
 // return 404 if the page doesn't have the needed prefix.
 func stripPrefix(prefix string, h http.Handler) http.Handler {
-	if prefix == "" {
+	if prefix == "" || prefix == "/" {
 		return h
 	}