title: can't find curl-config on NixOS
body: <p>I'm trying to install <a href="https://github.com/begriffs/haskell-vim-now" rel="noreferrer">vim-now-haskell</a> on NixOS 17.09.</p>
  
  <p>The installation fails with the exception</p>
  
  <pre><code>*** Installer requires 'curl-config'. Please install and try again.
  *** Aborting...
  </code></pre>
  
  <p>Unfortunately <a href="https://nixos.org/nixos/packages.html#curl-config" rel="noreferrer">Search NixOS packages</a> doesn't list any package for <code>curl-config</code>. It also isn't in installed <code>curl-7.56.1</code>.</p>
  
  <p>I can hardly believe NixOS doesn't provide <code>curl-config</code>. Therefore I'm looking here for help to find it.</p>