[Pkg-rust-maintainers] Bug#1017084: rust-chrono: please update to v0.4.21

[Peter Green]

> 
> ome reverse dependencies tightens dependency on chrono to v0.4.20 or
> v0.4.21, apparently related to RUSTSEC advisory 2020-0159 (bug#996913).

As I discussed in that bug report, while I understand why rustsec
consider this a security issue (they treat all soundness bugs as security
issues) I don't think it's particularly useful to characterise it as one
downstream.

> Please update to latest upstream release 0.4.21 to allow this security
> tightening to take effect in Debian-packaged code.

The new upstream version depends on the iana-time-zone crate, if/when
someone packages that crate and it passes trough NEW, I am happy to
update chrono.