Update mio requirement from 0.6.13 to 0.7.13

Updates the requirements on [mio](https://github.com/tokio-rs/mio) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/mio/releases)
- [Changelog](https://github.com/tokio-rs/mio/blob/v0.7.13/CHANGELOG.md)
- [Commits](tokio-rs/mio@v0.6.13...v0.7.13)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

Cargo.toml

@@ -18,7 +18,7 @@ rand = "0.6"
 tokio = "1.8"
 futures = "0.1"
 futures-cpupool = "0.1"
-mio = "0.6.13"
+mio = "0.7.13"
 aio-bindings = { path = "aio-bindings", version = "0.1.2" }
 libc = "0.2"
 memmap = "0.7.0"