Electron nix-shell FHS fiddlings

shell.nix

{
  pkgs ? import <nixpkgs> {},
  unstable ? import (fetchTarball https://nixos.org/channels/nixos-unstable/nixexprs.tar.xz) {},
  buildFHSUserEnv ? opt: (unstable.buildFHSUserEnv opt).env,
}:

buildFHSUserEnv rec {
  name = "electron-env";

  targetPkgs = p: (with pkgs;
    atomEnv.packages ++
    [
      gtk2-x11
      at-spi2-atk
      nodejs-8_x
      (yarn.override { nodejs = nodejs-8_x; })
    ]
  );

  extraBuildCommands = ''
    mv etc etc-
    ln -s /host/etc etc
  '';

  runScript = "${pkgs.zsh}/bin/zsh";
}