Fix incorrect <input> type for Date Picker example

Date Picker requires `type="text"`, but it was set to `type="date"` in the example (the actual component had the correct type).

jade/page-contents/forms_content.html

@@ -772,7 +772,7 @@ <h2 class="header">Date Picker</h2>
         <label for="birthdate">Birthdate</label>
         <input id="birthdate" type="text" class="datepicker">
         <pre><code class="language-markup">
-  &lt;input type="date" class="datepicker">
+  &lt;input type="text" class="datepicker">
         </code></pre>
 
         <h4>Initialization</h4>