Cardano Updates

* Prepare for switch from cryptonite to crypton

The former is deprecated in favor of the latter which is supposedly
a drop in replacement. However just doing the drop in replacement
does not work because when a package depends on cryptonite and
and dependency depends on crypton, GHC does not recognise a type
defined in the former as the same as a type defined in the latter.

The solution is to put an upper bound on the `cardano-cypto`
package to the last one using `cryptonite` and then release a
new version of `cardano-crypto` that switches to `crypton`.

* Nix updates