BP256 and BP384 v0.6.1 docs.rs build fails

[dnlmlr]

Just in case you weren't aware, the latest (v0.6.1) builds of bp256 and bp384 on docs.rs failed

• https://docs.rs/crate/bp256/0.6.1/builds/794021
• https://docs.rs/crate/bp384/0.6.1/builds/794027

[tarcieri]

Yeah, need to look into that