Online documentation for latest version is broken

[allgoewer]

Hi,

the documentation hosted at docs.rs/ seems to be broken.

[VorpalBlade]

This still seems to be an issue with the most recent version. From what I can tell this is due to attempting to use nightly features for the docs.rs build. I'm not sure why, as I thought docs.rs used nightly by default.

[ThalusA]

Build log : https://docs.rs/crate/embedded-svc/0.28.1/builds/1605897

[ivmarkov]

Build log : https://docs.rs/crate/embedded-svc/0.28.1/builds/1605897

If you open a PR to remove those, I'll merge.