trifecta: override dependency versions

"jailbreak" did not work for this package
Also, I force a downgrade for "hashable" to make stuff work with our current haskell platform. If you don't like running things "below spec", you can add the following to packageOverrides:

haskellPackages_ghc763 = pkgs.haskellPackages_ghc763.override {
  extraPrefs = self: {
    hashable = self.hashable_1_2_1_0;
  };
};