title: 'ng serve' does not work after a double install
body: <p>I used to have Angular CLI, but I mistakenly installed it again with</p>
  <pre class="lang-none prettyprint-override"><code>npm install -g angular-cli
  </code></pre>
  <p>And now when I run <code>ng serve</code> it complains:</p>
  <blockquote>
  <p>It seems like you're using a project generated using an old version of the Angular CLI.</p>
  <p>The latest CLI now uses webpack and includes a lot of improvements, include a simpler
  workflow, a faster build and smaller bundles.</p>
  <p>To get more info, including a step-by-step guide to upgrade the CLI, follow this link:
  <a href="https://github.com/angular/angular-cli/wiki/Upgrading-from-Beta.10-to-Beta.12" rel="nofollow noreferrer">https://github.com/angular/angular-cli/wiki/Upgrading-from-Beta.10-to-Beta.12</a></p>
  </blockquote>
  <p>When I try to create a new project using <code>ng new</code> in another directory, it complains that:</p>
  <blockquote>
  <p>Cannot find module 'reflect-metadata'</p>
  </blockquote>
  <p>So what is the problem?</p>