Shell.nix cleanup.

shell.nix

@@ -1,25 +1,32 @@
+{ pkgs ? import <nixpkgs> {
+  overlays = [
+    (import (builtins.fetchTarball
+      "https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz"))
+  ];
+} }:
+with pkgs;
 let
-  moz_overlay = import (builtins.fetchTarball
-    "https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz");
 
-  nixpkgs = import <nixpkgs> { overlays = [ moz_overlay ]; };
-
-  nightly = ((nixpkgs.rustChannelOf {
+  nightly = ((pkgs.rustChannelOf {
     date = "2019-09-01";
     channel = "nightly";
   }).rust.override {
     extensions = [
-      "rust-src"
-      "rls-preview"
       "clippy-preview"
+      "rls-preview"
       "rust-analysis"
+      "rust-src"
       "rustfmt-preview"
     ];
   });
 
-in with nixpkgs;
-stdenv.mkDerivation {
+  nu-deps = [ openssl_1_1 pkg-config x11 python3 ];
+
+  rust = [ nightly rustracer cargo-watch ];
+
+in stdenv.mkDerivation {
   name = "nushell-rust";
-  buildInputs = [ nightly openssl_1_1 pkg-config rustracer ];
+  buildInputs = nu-deps ++ rust;
   RUST_SRC_PATH = "${nightly}/lib/rustlib/src/rust/src";
+  SSL_CERT_FILE = "/etc/ssl/certs/ca-certificates.crt";
 }