Fix "expand all sections" second link

Issue was that the jQuery is using .children() to add the event handlers but due
to some changes to the HTML, the second link is no longer a direct child. I've
switched this to .find() instead.

conservancy/static/js/supporter-page.js

@@ -158,7 +158,7 @@ $(document).ready(function() {
         $element.append($element.data('expand-link-text'));
     });
     $('.expandable-section').each(function(index) {
-        var $expandlink = $(this).children('a.expander');
+        var $expandlink = $(this).find('a.expander');
         var $ourexpandablesection = $(this);
         $expandlink.on('click', function(event) {
             $expandlink.fadeOut('slow');