Merge branch 'nix-shell-maybe-this-you-mean' into 'develop'

nix-shell: Make overloadable, use old morph for now

See merge request privatestorage/PrivateStorageio!111

shell.nix

@@ -4,7 +4,7 @@ let
 in
 { pkgs ? nixpkgs }:
 pkgs.mkShell {
-  NIX_PATH = "nixpkgs=${nixpkgs.path}";
+  NIX_PATH = "nixpkgs=${pkgs.path}";
   buildInputs = [
     pkgs.morph
     stable2105.vagrant