Switch from haskell-crypto to haskell-cryptonite

Haskell-Crypto is broken with GHC 8.6[1][2], so switch over to cryptonite
which is the de-facto crypto library for Haskell nowadays.

[1] https://gitlab.haskell.org/ghc/ghc/issues/16406
[2] https://bugs.debian.org/945931