title: Polymer paper-input binding always text
body: <p>I have the following polymer element:</p>
  
  <pre><code>&lt;link rel="import" href="../bower_components/polymer/polymer.html"&gt;
  &lt;link rel="import" href="../bower_components/paper-input/paper-input.html"&gt;
  &lt;link rel="import" href="../bower_components/iron-input/iron-input.html"&gt;
  
  &lt;dom-module id="number-input"&gt;
      &lt;template&gt;
          &lt;paper-input type="number" label="amount" value="{{amount}}"&gt;&lt;/paper-input&gt;
      &lt;/template&gt;
      &lt;script&gt;
          Polymer({
              is: "number-input",
              properties: {
                  amount: {
                      type: Number,
                  }
              }
          });
      &lt;/script&gt;
  &lt;/dom-module&gt;
  </code></pre>
  
  <p>The "amount" property is always a string. Even though I define the property as a "Number". Am I missing something or is this normal behaviour ?</p>
  
  <p>Sander.</p>