hackage2nix.hs: re-enable fixed hruby build
hackage2nix.hs: re-enable fixed hruby build

Relates to https://github.com/NixOS/nixpkgs/pull/7442.

jb55/cabal2nix,bennofs/cabal2nix,dmalikov/cabal2nix,psibi/cabal2nix,gridaphobe/cabal2nix,spencerjanssen/cabal2nix,Fuuzetsu/cabal2nix