hackage-packages.nix: update Haskell package set

This update was generated by hackage2nix v20150922-6-g5d5ccfe using the following inputs:

  - Nixpkgs: https://github.com/NixOS/nixpkgs/commit/f21f116631be9905ba96af24024fb506e1e65325
  - Hackage: https://github.com/commercialhaskell/all-cabal-hashes/commit/f8855b5494a1df4f7b93142a19d944f10380a75c
  - LTS Haskell: https://github.com/fpco/lts-haskell/commit/831a37566be736e827a8f17d6c006a09ed384cd6
  - Stackage Nightly: https://github.com/fpco/stackage-nightly/commit/96ef887f310857f0d01e91995b9a4ecc938d434b