Update hpack.cabal to file generated by main branch version of Hpack

[mpilgrem]

The main branch version of Hpack renders hpack.cabal differently from the file in the repository.

[sol]

The main branch version of Hpack renders hpack.cabal differently from the file in the repository.

@mpilgrem This is only true if you either passed --canonical to hpack, or if you deleted the existing hpack.cabal.

Hpack extract formatting hints from any existing .cabal file and reproduce the new .cabal file using those formatting hints. This results in smaller git diffs and as a result makes it easier to spot any differences when migrating an existing Cabal project to Hpack.