[Pkg-rust-maintainers] Bug#1013139: rust-pbkdf2: please upgrade to v0.7

[Peter Green]

> Please upgrade to upstream branch v0.7, needed by projects I am
> preparing for Debian.

Do you need 0.7 specifically or would the latest version work for
you?

Also it looks like newer versions of this crate have an optional
but enabled by default dependency on password-hash which is not
currently in Debian. I'm reluctant to patch out enabled by default
features because it has the potential for causing unexplained build
failures downstream.