dhall-grafana: Fix Prelude dependency. (#144915)
dhall-grafana: Fix Prelude dependency. (#144915)

At init, dhall-grafana would not compile because it has a dependency
on Prelude version 19.  Upstream merged a patch to bring it's Prelude
dependency up to nixpkgs.
NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs