Including .clippy.toml in crate tarball leads to older clippy versions failing

[jplatte]

… even on crates that have slab as a dependency. cargo-diet might help setting a reasonable include / exclude value in Cargo.toml / [package]. Otherwises here's the docs for those settings.

[taiki-e]

This is definitely a clippy bug, but I would accept the patch to exclude the top-level hidden files/dirs, like my projects do.