title: NixOS install specific NodeJS version
body: <p>I can see that NixOS has these versions available for install:</p>
  
  <pre><code>...
  nodejs-0.10-statsd-0.7.2
  nodejs-0.10.42
  nodejs-4.3.1
  nodejs-5.9.0
  ...
  </code></pre>
  
  <p>yet systemPackages doesn't like me installing <code>nodejs-5.9.0</code> as it complains that:</p>
  
  <pre><code>error: syntax error, unexpected INT, expecting ID or OR_KW or DOLLAR_CURLY or '"', at /etc/nixos/configuration.nix:49:14
  (use ‘--show-trace’ to show detailed location information)
  error: syntax error, unexpected INT, expecting ID or OR_KW or DOLLAR_CURLY or '"', at /etc/nixos/configuration.nix:49:14
  (use ‘--show-trace’ to show detailed location information)
  building the system configuration...
  error: syntax error, unexpected INT, expecting ID or OR_KW or DOLLAR_CURLY or '"', at /etc/nixos/configuration.nix:49:14
  (use ‘--show-trace’ to show detailed location information)
  </code></pre>
  
  <p>which suggests to me I'm doing something wrong. I'd rather not just install with <code>nix-env -i ...</code> because I want it system-wide (and I'm building my standard NixOS configuration for all my dev' machines).</p>
  
  <p>According to the <a href="https://github.com/NixOS/nixpkgs/tree/master/pkgs/development/web/nodejs" rel="noreferrer">nixpkgs repository</a> v6 is available, but I've no idea how to tell <code>nixos-rebuild</code> through configuration.nix or otherwise how to install it.</p>
  
  <p>How can I configure this properly so I can install the latest version of NodeJS, or 5.9.0 specifically?</p>