Cannot override notion with package from unstable

Question

The latest version of notion is available in the unstable branch. I want my install of nixos 17.03 to use it. Here is my configuration.

I override notion with pkgsUnstable.notion.

nixpkgs.config = {
  allowUnfree = true;
  packageOverrides = let pkgsUnstable = import (
    fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable.tar.gz
  ) { }; in pkgs:
  rec {
    visualvm = pkgsUnstable.visualvm;
    notion = pkgsUnstable.notion;
  };
};

And I added notion to environment.systemPackages. I also have services.xserver.winowManager.notion.eable = true;

With this setup I can get visualvm updated from unstable but when I check the version of notion with notion -version I get 3-2015061300. It should be 3-2017050501.

How can I get the updated version of notion?