http-body-util failing doc generation #174

After rust-lang/rust#138907 new Rust versions reject the attribute doc_auto_cfg when generating docs. This attribute is used by http-body-util and so the crate's docs https://docs.rs/crate/http-body-util/latest aren't available, also affecting the nightly doc generation of upstream crates depending on http-body-util that wanna include downstream docs in the doc generation.

The fix is just to migrate that attribute to doc_cfg