Bump ghc-artefact-nix

This fixes the bindist versioning logic.

scripts/build-all.nix

@@ -12,10 +12,10 @@ let
   # GHC from the given bindist.
   ghc =
     let
-      commit = "633c6d7553d0f2c91245bcf47ae539cfdb7aaa13";
+      commit = "027df18eb894ef622f67b2f487a851dc534403e3";
       src = fetchTarball {
         url = "https://github.com/bgamari/ghc-artefact-nix/archive/${commit}.tar.gz";
-        sha256 = "0yl7dk8drb92ipgph1mxx8my4gy9py27m749zw6ah6np4gvdp9sx";
+        sha256 = "0ijdpqsg8b7hz89hpgmpzfvg70y6yfq4wrqgngvqlfri5hy9fmg3";
       };
     in nixpkgs.callPackage "${src}/artifact.nix" {} {
       ncursesVersion = "6";