Bumping hackage breaks cabal

[Chris Warburton]

I tried bumping mkStableHackageDb.nix with the following:

    { rev    ? "c5d1a03",
      sha256 ? "18m1l1nlshbn0r0x5a5n89brvsc4jb2g4z9xpiyvn9cgaqh95pf6" }:

After waiting a while for it to be generated, cabal-install 1.24.0.2
(nixpkgs1703.cabal-install) and from nixpkgs1609 both complained about
the hackage index being broken:

    Resolving dependencies...
    cabal: internal error when reading package index: failed to parse .cabal
    fileThe package index or index cache is probably corrupt. Running cabal update
    might fix it.

This may be due to .cabal files using a newer, unsupported format.