nixos-rebuild switch error

[chessai@CHESSAI:~]$ sudo nixos-rebuild switch             
[sudo] password for chessai: 
building Nix...
building the system configuration...
error: attribute ‘github:enomsg/vim-haskellConcealPlus’ missing, at /nix/store/5ixbx59nm70kgb2dcwqlndaxvwwy1r4h-nixos-18.03pre116432.263185aa68/nixos/pkgs/misc/vim-plugins/vim-utils.nix:159:25
(use ‘--show-trace’ to show detailed location information)

referenced nixpkgs links

nix with vam/pathogen tutorial:
  https://github.com/NixOS/nixpkgs/blob/master/pkgs/misc/vim-plugins/vim-utils.nix
vim-plugin-names:
   https://github.com/NixOS/nixpkgs/blob/master/pkgs/misc/vim-plugins/vim-plugin-names
   

vim.nix

{config,pkgs,...}:

let
  myVim = pkgs.vim_configurable.customize {
    name = "vim";
    vimrcConfig = {
      customRC = ''
        syntax on
        filetype plugin indent on
        
        set nocompatible
        set number
        set nowrap
        set showmode
        set tw=80
        set smartcase
        set smarttab
        set smartindent
        set autoindent
        set softtabstop=2
        set shiftwidth=2
        set expandtab
        set incsearch
        set mouse=a
        set history=1000
        set clipboard=unnamedplus,autoselect

        set completeopt=menuone,menu,longest
        
        set wildignore+=*\\tmp\\*,*.swp,*.swo,*.zip,.git,.cabal-sandbox
        set wildmode=longest,list,full
        set wildmenu
        set completeopt+=longest

        set t_Co=256
      '';
       vam.pluginDictionaries = [
        {
          names = [ 
            "Gist"
            "Hoogle"
            "Syntastic"
            "The_NERD_Commenter"
            "The_NERD_tree"
            "ghcmod" 
            "github:enomsg/vim-haskellConcealPlus"
            "github:flazz/vim-colorschemes"
            "rainbow_parentheses" 
            "vundle" ];
        }
      ];
    };
  };
in
{
  environment.systemPackages = [ myVim ];
  environment.shellAliases.vi = "vim";
  environment.variables.EDITOR = "vim";
  programs.bash.shellAliases = {
    vi = "vim";
  };
}