title: npm doesn't update tsc version
body: <p>Typescript is updated using the following command:</p>
  
  <pre><code>npm install typescript -g
  </code></pre>
  
  <p>And latest version 2.4.2 is installed correctly and I can verify it by looking the path shown by folloing command:</p>
  
  <pre><code>npm list typescript -g
  </code></pre>
  
  <p>but the following command shown older version (1.0.3.0) :</p>
  
  <pre><code>tsc -v
  </code></pre>
  
  <p>Also looked in TEMP variable and it points to the same path as it showed by <code>npm list</code>. </p>
  
  <p>Also running <code>where tsc</code> in command prompt doesn't show anything and doesn't come up with any error.</p>