title: Observer not responding to <paper-input> in Polymer 2.x
body: <p>I want to trigger an observer by entering text into a <code>&lt;paper-input&gt;</code> field.</p>
  
  <p>When entering text into the zip code field, I expect to see the entered text logged to the console. Instead, I do not see anything in the console.</p>
  
  <p>What am I doing wrong?</p>
  
  <p><a href="http://jsbin.com/xahobojixe/1/edit?html,console,output" rel="nofollow noreferrer">Here is the JSbin Demo.</a></p>
  
  <a href="http://jsbin.com/xahobojixe/1/edit?html,console,output" rel="nofollow noreferrer">http://jsbin.com/xahobojixe/1/edit?html,console,output</a>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  
    &lt;head&gt;
      &lt;meta charset="utf-8"&gt;
      &lt;meta name="viewport" content="width=device-width"&gt;
      &lt;title&gt;JS Bin&lt;/title&gt;
  
      &lt;base href="//polygit.org/polymer+:master/components/"&gt;
      &lt;script src="webcomponentsjs/webcomponents-lite.js"&gt;&lt;/script&gt;
      &lt;link rel="import" href="polymer/polymer-element.html"&gt;
      &lt;link rel="import" href="paper-input/paper-input.html"&gt;
  
    &lt;/head&gt;
  
    &lt;body&gt;
  
      &lt;dom-module id="my-el"&gt;
        &lt;template&gt;
          &lt;paper-input label="simple character counter" char-counter value="{{zipCode}}"&gt;&lt;/paper-input&gt;
          [[zipCode]]
        &lt;/template&gt;
  
        &lt;script&gt;
          class MyEl extends Polymer.Element {
            static get is() {
              return 'my-el';
            }
  
            static get properties() {
              /**/
              return {
                properties: {
                  zipCode: {
                    type: String,
                    notify: true,
                    observer: '_zipCodeChanged',
                  },
                },
              };
            }
  
            constructor() {
              super();
            }
  
            /**/
            ready() {
              super.ready();
            }
  
            _zipCodeChanged(s) {
              console.log('zip-code', s);
              console.log('zip-code-this', this.zipCode);
            }
  
          }
  
          window.customElements.define(MyEl.is, MyEl);
  
        &lt;/script&gt;
      &lt;/dom-module&gt;
  
      &lt;my-el&gt;&lt;/my-el&gt;
    &lt;/body&gt;
  
  &lt;/html&gt;
  </code></pre>