Bump mio from 0.6.18 to 0.6.19
Bump mio from 0.6.18 to 0.6.19

Bumps [mio](https://github.com/carllerche/mio) from 0.6.18 to 0.6.19.
- [Release notes](https://github.com/carllerche/mio/releases)
- [Changelog](https://github.com/tokio-rs/mio/blob/v0.6.19/CHANGELOG.md)
- [Commits](https://github.com/carllerche/mio/compare/v0.6.18...v0.6.19)
alex/otp-cop