news updates: use relative time instead of date.

Use relative time on site updates to show when a site update was posted
("5m ago"), instead of the date ("Oct 1").

app/views/news_updates/_listing.html.erb

@@ -2,7 +2,7 @@
   <div id="news-updates" data-id="<%= NewsUpdate.recent.first.try(:id) %>" style="display: none;">
     <ul>
       <% NewsUpdate.recent.each do |news_update| %>
-        <li><%= news_update.created_at.strftime("%b %d") %>: <%= news_update.message.html_safe %></li>
+        <li><%= time_ago_in_words_tagged(news_update.created_at, compact: true) %> ago: <%= news_update.message.html_safe %></li>
       <% end %>
     </ul>