Bump libc from 0.2.56 to 0.2.57
Bump libc from 0.2.56 to 0.2.57

Bumps [libc](https://github.com/rust-lang/libc) from 0.2.56 to 0.2.57.
- [Release notes](https://github.com/rust-lang/libc/releases)
- [Commits](https://github.com/rust-lang/libc/compare/0.2.56...0.2.57)
alex/otp-cop