Get better cross-package links in the Haddock docs

Building the dependency docs lets Haddock generate links into them.

lib.nix

@@ -150,7 +150,7 @@ rec {
           text = ''
             set -x
             sdist=$(cabal sdist | tail -n 1)
-            haddocks=$(cabal haddock --haddock-for-hackage | tail -n 1)
+            haddocks=$(cabal haddock --enable-doc --haddock-for-hackage | tail -n 1)
             cabal upload "$@" "$sdist"
             cabal upload "$@" --documentation "$haddocks"
           '';