Use a recent Nixpkgs release and fix the Nix build

default.nix

@@ -1,10 +1,10 @@
 let
-  pkgs = import (builtins.fetchGit {
-     url = git://github.com/NixOS/nixpkgs;
-     rev = "8c6f9223d02c5123cbd364d6d56caca3c81416f0";
+  pkgs = import (fetchTarball {
+    url = https://github.com/NixOS/nixpkgs/archive/642499faefb17c3d36e074cf35b189f75ba43ee2.tar.gz;
+    sha256 = "16j7gl3gg839fy54z5v4aap8lgf1ffih5swmfk62zskk30nwzfbi";
   }) {};
 
 in
 
-import ./nimbus.nix { inherit pkgs; }
+import ./nix/nimbus.nix { inherit pkgs; }
 

nix/nim.nix

@@ -42,11 +42,13 @@ stdenv.mkDerivation rec {
     openssl pcre readline sqlite git
   ];
 
-  buildPhase   = ''
-    export HOME=$TMP
-    export GIT_SSL_CAINFO=/etc/ssl/certs/ca-certificates.crt
-    sh build_all.sh
-  '';
+  buildPhase   =
+    let caBundle = ./ca-bundle.pem;
+    in ''
+      export HOME=$TMP
+      export GIT_SSL_CAINFO=${caBundle}
+      sh build_all.sh
+    '';
 
   installPhase = ''
     install -Dt $out/bin bin/* koch