Remove OCaml 5 warning

[samoht]

Otherwise got:

File "_none_", line 1:
Alert ocaml_deprecated_auto_include:
OCaml's lib directory layout changed in 5.0. The unix subdirectory has been
automatically added to the search path, but you should add -I +unix to the
command-line to silence this alert (e.g. by adding unix to the list of
libraries in your dune file, or adding use_unix to your _tags file for
ocamlbuild, or using -package unix for ocamlfind).

[dinosaure]

Thanks