staticfiles: Re-allow HEAD requests

caddyhttp/staticfiles/fileserver.go

@@ -53,7 +53,7 @@ type FileServer struct {
 
 // ServeHTTP serves static files for r according to fs's configuration.
 func (fs FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
-	if r.Method != "GET" {
+	if r.Method != "GET" && r.Method != "OPTIONS" {
 		return http.StatusMethodNotAllowed, nil
 	}
 	return fs.serveFile(w, r)