Changes: * replace `iotuil` elements with the ones from `os` package; * replace `os.Filemode` with `fs.FileMode`; * use `signal.NotifyContext` instead of `NewGracefulContext` (removed). Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>