cargo-fmt: Take into account the edition for each target
cargo-fmt: Take into account the edition for each target

When formatting the crate, with `cargo fmt`, it parses each target
with the specific Rust edition.

Fixes: #3104.

Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,rust-lang/rustfmt,graydon/rust,SingingTree/rustfmt,rust-lang/rustfmt,aidancully/rust,graydon/rust,aidancully/rust,SingingTree/rustfmt