title: ReferenceError: Polymer is not defined
body: <p>When i start <code>gulp serve</code> am facing following error</p>
  
  <blockquote>
    <p>ReferenceError: Polymer is not defined
    <a href="http://localhost:5000/elements/my-greeting/my-greeting.html:30" rel="nofollow noreferrer">http://localhost:5000/elements/my-greeting/my-greeting.html:30</a></p>
  </blockquote>
  
  <p>ReferenceError: Polymer is not defined
  <a href="http://localhost:5000/elements/my-list/my-list.html:30" rel="nofollow noreferrer">http://localhost:5000/elements/my-list/my-list.html:30</a></p>
  
  <p>Here is code of my-greeting.</p>
  
  <pre><code> &lt;script&gt;
  (function() {
    'use strict';
  
    Polymer({
      is: 'my-greeting',
  
      properties: {
        greeting: {
          type: String,
          value: 'Welcome!',
          notify: true
        }
      }
    });
  })();
  &lt;/script&gt;
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/hDUIh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hDUIh.png" alt="Check Image of blank page with error"></a></p>