nix: Use GHC 8.10.4 in Nix build environment

default.nix

@@ -3,7 +3,7 @@ let
     "postgrest";
 
   compiler =
-    "ghc884";
+    "ghc8104";
 
   # PostgREST source files, filtered based on the rules in the .gitignore files
   # and file extensions. We want to include as litte as possible, as the files
@@ -109,7 +109,7 @@ rec {
   # Tooling for analyzing Haskell imports and exports.
   hsie =
     pkgs.callPackage nix/hsie {
-      ghcWithPackages = pkgs.haskell.packages."${compiler}".ghcWithPackages;
+      ghcWithPackages = pkgs.haskell.packages.ghc884.ghcWithPackages;
     };
 
   ### Tools