Update sysctl requirement from ~0.2.0 to ~0.3.0

Updates the requirements on [sysctl](https://github.com/johalun/sysctl-rs) to permit the latest version.
- [Release notes](https://github.com/johalun/sysctl-rs/releases)
- [Changelog](https://github.com/johalun/sysctl-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/johalun/sysctl-rs/commits)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Author: dependabot-support

Cargo.toml

@@ -25,7 +25,7 @@ bitflags = "^1"
 byteorder = "^1.2.3"
 failure = "~0.1.1"
 libc = "~0.2.41"
-sysctl = "~0.2.0"
+sysctl = "~0.3.0"
 nix= "^0.12.0"
 rctl = "0.0.5"
 strum = "0.13.0"