hackage-packages.nix: update Haskell package set

This update was generated by hackage2nix v20150922-8-g2bcda7a using the following inputs:

  - Nixpkgs: https://github.com/NixOS/nixpkgs/commit/8af2f6e9c4c5000b3964c56d1221441d20e96caf
  - Hackage: https://github.com/commercialhaskell/all-cabal-hashes/commit/db7872f2645708ddb074707fe7e584f1f2356103
  - LTS Haskell: https://github.com/fpco/lts-haskell/commit/831a37566be736e827a8f17d6c006a09ed384cd6
  - Stackage Nightly: https://github.com/fpco/stackage-nightly/commit/e5598095e13c11845dadd154afd204ada3ea4c35