Update the chrono crate to get rid of an old time 0.1 dependency

Getting rid of the old time 0.1 dependency is desirable as it isn't
maintained anymore and triggers security alerts due CVE-2020-26235 [0].

The chrono crate finally dropped the dependency on time in version
0.4.30 [1].

[0]: https://github.com/science-computing/butido/security/dependabot/4
[1]: chronotope/chrono#602 (comment)

Signed-off-by: Michael Weiss <michael.weiss@atos.net>