title: Having error "Module 'name' resolves to an untyped module at..." when writing custom TypeScript definition file
body: <p>I can't find TypeScript definition <code>@type/{name}</code> for one of my installed NodeJS packages, so I attempt to write a <code>d.ts</code> file for it, and put the file in <code>{project root}\typings</code> folder. This is how I do:</p>
  
  <pre><code>// My source code: index.ts
  import Helper from 'node-helper-lib';
  
  
  // My definition: \typings\node-helper-lib.d.ts
  declare....(something else)
  
  declare module 'node-helper-lib' {
     class Helper { ... }
     export = Helper;
  }
  </code></pre>
  
  <p>However, Visual Studio Code keeps yielding this error and puts red line under <code>declare module 'node-helper-lib'</code>:</p>
  
  <blockquote>
    <p>[ts] Invalid module name in augmentation. Module 'node-helper-lib'
    resolves to an untyped module at '{project
    path}\node_modules\node-helper-lib\index.js', which cannot be
    augmented.</p>
  </blockquote>
  
  <p>Isn't it legit that because the library is untyped, so I should be allowed to add typing to it?</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>I am using:</p>
  
  <ul>
  <li>TypeScript: 2.1.4</li>
  <li>Visual Studio Code: 1.9.1</li>
  <li>Node JS: 6.9.4</li>
  <li>Windows 10 x64</li>
  </ul>