Version 1.0.26 causes Clippy warnings on older versions of Rust

[YuhanLiin]

The newest release, 1.0.26, causes Clippy warnings on versions of Rust that precede the nonstandard_macro_braces lint. Specifically, the warning unknown clippy lint: clippy::nonstandard_macro_braces pops up in places with derive(Error). This breaks CI builds that use Clippy and have an MSRV older than nonstandard_macro_braces.

[damianwadley]

See #140, where I'm still hoping @dtolnay will consider reverting the change.

[damianwadley]

Looks like nonstandard_macro_braces is available from Rust 1.51.

@dtolnay Can we get a response? Whether you are able to revert a change that is no longer needed and is causing actual semver problems for people still on Rust <=1.50 that are trying to use your library, or whether you want to disregard anyone using versions of Rust that are more than a few months old? Please consider that there are developers out there who only have the time and opportunity to upgrade through Rust versions maybe two or three times a year.

Not looking for a service contract covering years of maintenance, here. Just to undo a couple commits that aren't doing anything helpful anymore.

[danieleades]

looks like this was fixed upstream in clippy - rust-lang/rust-clippy#7431

i think this can probably be closed