do not create a fresh instance of nixpkgs

Reuse the passed instance of nixpkgs instead of re-evaluating
and creating a new instance. See zimbatm's "1000 instances of
nixpkgs" for backround info.

flake.nix

@@ -13,13 +13,13 @@
     # provide db-package for all archs, but scaper/test only for most common
     (utils.lib.eachSystem utils.lib.allSystems (system:
       let
-        pkgs = import nixpkgs { inherit system; };
+        pkgs = nixpkgs.legacyPackages.${system};
       in
       nixpkgs.lib.recursiveUpdate
         (nixpkgs.lib.optionalAttrs (builtins.elem system utils.lib.defaultSystems) rec {
           packages.updater = pkgs.callPackage ./updater.nix {};
           apps.updater = { type = "app"; program = "${packages.updater}/bin/updater";};
-          devShell = with pkgs; mkShell {
+          devShells.default = with pkgs; mkShell {
             buildInputs = [ nim nimble-unwrapped nimlsp ];
           };
           checks.vmtest = import ./test.nix { inherit pkgs; flake = self; };  # nixpkgs must be set to a revision present in the JSON file
@@ -33,4 +33,4 @@
     {
       nixosModules.programs-sqlite = pass@{ pkgs, ... }: (import ./module.nix { programs-sqlite = (getDB pkgs); }) pass;
     };
-}
+}