title: Define scoped npm registry URL as environment variable
body: <p>We have a scoped module, and for <code>npm</code> to be be able to resolve it, we have to say where its repo is. This can be done in i.e. <code>.npmrc</code>, such as:</p>
  
  <pre><code>@my-scope:registry=http://my-sweet-replication.example.com/npm/
  </code></pre>
  
  <p>My problem is that because of some proxying and authentication for GET requests, I have to put different values in <code>.npmrc</code> for development versus the build server (travis enterprise). We already take advantage of the fact that <code>npm</code> can read environment variables for packages that are not scoped, but as both <code>@</code> and <code>:</code> are invalid characters in an environment variable I'm unable to export the correct URL.</p>
  
  <p>Any ideas on how to tell npm where to look for scoped modules without putting it in <code>.npmrc</code>?</p>