[ Fix ] pinning reference fix.

pin.nix

 {
-  hostPkgs ? import <nixpkgs> {},
   jsonpath,
-  depset ? {}
+  depset ? {},
+  hostPkgs ? import (builtins.fetchTarball {
+      name = "nixos-18.03";
+      url = https://github.com/nixos/nixpkgs/archive/18.03.tar.gz;
+      sha256 = "0hk4y2vkgm1qadpsm4b0q1vxq889jhxzjx3ragybrlwwg54mzp4f";
+    }) {}
 }:
   let
     pinnedVersion = hostPkgs.lib.importJSON jsonpath;

pkgs/default.nix

 {
-  hostPkgs  ? import <nixpkgs> {},
-  kapack       ? import ../pin.nix { inherit hostPkgs; jsonpath=../kapack.json; depset = {inherit hostPkgs;};},
-  pkgs         ? import ../pin.nix { inherit hostPkgs; jsonpath=../nixpkgs-18.03.json; },
+  pkgs         ? import ../pin.nix { jsonpath=../nixpkgs-18.03.json; },
+  kapack       ? import ../pin.nix { jsonpath=../kapack.json; depset = {hostPkgs=pkgs;};},
 }:
 let
   gitpin = f: pkgs.fetchgit {inherit (pkgs.lib.importJSON f) url sha256 rev fetchSubmodules;};