haskellPackages.dhall_1_28_0: fix overrides so it builds

This PR fixes dhall_1_28_0, dhall-bash_1_0_25, and dhall-json_1_6_0 so
they build.

They all require a newer version of prettyprinter than we get from the
LTS package set.

This is from https://github.com/NixOS/nixpkgs/pull/75931

 by @ijaketak.

Co-authored-by: Keito Kajitani <ijaketak@gmail.com>