Bump env_logger from 0.3.5 to 0.7.1

Bumps [env_logger](https://github.com/sebasmagri/env_logger) from 0.3.5 to 0.7.1.
- [Release notes](https://github.com/sebasmagri/env_logger/releases)
- [Changelog](https://github.com/sebasmagri/env_logger/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sebasmagri/env_logger/commits/v0.7.1)

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

Author: dependabot-preview[bot]

Cargo.lock

@@ -13,5 +13,5 @@ clap = "2"
 chan = "~0.1.0"
 chan-signal = "~0.1.0"
 log = "0.3"
-env_logger = "0.3"
+env_logger = "0.7"
 isatty = "0.1"