Bump log from 0.3.6 to 0.4.8

Bumps [log](https://github.com/rust-lang/log) from 0.3.6 to 0.4.8.
- [Release notes](https://github.com/rust-lang/log/releases)
- [Changelog](https://github.com/rust-lang-nursery/log/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/log/commits)

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

Author: dependabot-preview[bot]

Cargo.lock

@@ -12,6 +12,6 @@ irc = "0.13"
 clap = "2"
 chan = "~0.1.0"
 chan-signal = "~0.1.0"
-log = "0.3"
+log = "0.4"
 env_logger = "0.3"
 isatty = "0.1"