refactor/polish ~ convert to `try!` to `?` syntax
refactor/polish ~ convert to `try!` to `?` syntax

- convert to newer `?` syntax, fixing compiler warnings

+ requires MinSRV >= v1.13.0

.# [why]

The `?` operator was stabilized in rust v1.13.0.

Warnings requesting conversion from the old `try!` macro to the `?` operator
were introduced in rust v1.39.0.

* ref: <https://github.com/rust-lang/rust/blob/master/RELEASES.md>

uutils/coreutils,uutils/coreutils,uutils/coreutils