update examples

src/fs.c

@@ -1,6 +1,7 @@
 #include "fs.h"
 #include "printf.h"
 #include "str.h"
+#include "util.h"
 
 struct mg_fd *mg_fs_open(struct mg_fs *fs, const char *path, int flags) {
   struct mg_fd *fd = (struct mg_fd *) mg_calloc(1, sizeof(*fd));