swap lcoal function

enhanced-file-server.go

@@ -715,7 +715,7 @@ type fileHandler struct {
 // As a special case, the returned file server redirects any request
 // ending in "/index.html" to the same path, without the final
 // "index.html".
-func FileServer(root http.FileSystem) http.Handler {
+func FileServer(root FileSystem) http.Handler {
 	return &fileHandler{root}
 }