Fix function label: UnixLabels.sendto_substring s/bug/buf (#917)
Fix function label: UnixLabels.sendto_substring s/bug/buf (#917)

A label called ~bug is likely a typo
No change entry needed
msprotz/ocaml,msprotz/ocaml,yunxing/ocaml,yunxing/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,yunxing/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,msprotz/ocaml,yunxing/ocaml,yunxing/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml