tech(nix): Allow broken as retrie is marked as broken (#331)

See #325 for more information

Author: Julien Debon

shell.nix

@@ -16,7 +16,9 @@
 #    assuming that cabal new-build does succeed outside nix-shell
 
 { sources ? import nix/sources.nix,
-  nixpkgs ? import sources.nixpkgs {},
+  # TODO Remove allowBroken once retrie is no longer marked as broken in Nixpkgs
+  # See https://github.com/haskell/haskell-language-server/issues/325
+  nixpkgs ? import sources.nixpkgs { config.allowBroken = true; },
   compiler ? "default",
   hoogle ? false
  }: