Date Picker Spin Button Example: fix query selector (pull #1153)

Resolves issue #1151. The query selector for the `spinbutton` element was incomplete, which caused it to not query properly in Safari or IE.

This fix adds in the missing characters to the query so that it queries properly.

examples/spinbutton/js/spinbutton-date.js

@@ -14,7 +14,7 @@ var SpinButtonDate = function (domNode, values, callback)  {
 
   var initialValue = domNode.getAttribute('aria-valuetext');
 
-  this.spinbuttonNode = domNode.querySelector('[role="spinbutton');
+  this.spinbuttonNode = domNode.querySelector('[role="spinbutton"]');
 
   this.previousValueNode = domNode.querySelector('.previous');
   this.nextValueNode = domNode.querySelector('.next');