Future incompatibility warning because of dependency on nom 1.2.4

[mtkennerly]

Using Rust 1.68.0, this warning is displayed while building:

warning: the following packages contain code that will be rejected by a future version of Rust: nom v1.2.4

Sample reason:

$ cargo report future-incompatibilities --id 359 --package nom@1.2.4
> warning: trailing semicolon in macro used in expression position
>    --> C:\Users\mtken\.cargo\registry\src\github.com-1ecc6299db9ec823\nom-1.2.4\src\macros.rs:482:40
>     |
> 482 |     map_impl!($i, call!($f), call!($g));
>     |                                        ^
>     |
>    ::: C:\Users\mtken\.cargo\registry\src\github.com-1ecc6299db9ec823\nom-1.2.4\src\nom.rs:329:3
>     |
> 329 |   map!(i, be_u8, | x | { x as i8 })
>     |   --------------------------------- in this macro invocation
>     |
>     = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
>     = note: for more information, see issue #79813 <https://github.com/rust-lang/rust/issues/79813>
>     = note: macro invocations at the end of a block are treated as expressions
>     = note: to ignore the value produced by the macro, add a semicolon after the invocation of `map`
>     = note: `#[allow(semicolon_in_expressions_from_macros)]` on by default
>     = note: this warning originates in the macro `map` (in Nightly builds, run with -Z macro-backtrace for more info)