hackage-packages.nix: update Haskell package set

This update was generated by hackage2nix v20150922-23-g9db0d61 using the following inputs:

  - Nixpkgs: https://github.com/NixOS/nixpkgs/commit/1146c867e3e1ff9118358139680913731194d6f8
  - Hackage: https://github.com/commercialhaskell/all-cabal-hashes/commit/1791c0e4149a511717daf4438fefa7e355f25f86
  - LTS Haskell: https://github.com/fpco/lts-haskell/commit/4622b913dcfa6d442d875c8604a87cc79884f74c
  - Stackage Nightly: https://github.com/fpco/stackage-nightly/commit/f51b9b15137c1e15d40618c10971202f106514c4