Add .jumbotron to #pre-release.

docs/announcements-4.0.html

@@ -3,13 +3,9 @@ layout: default
 title: Select2 4.0.0 Released
 slug: announcements-4.0
 ---
-
-<div class="container">
-  <section id="pre-release">
+<section id="pre-release" class="jumbotron">
+  <div class="container">
     <h1>Pre-release notes</h1>
-
-    <hr />
-
     <p class="lead">
       The 4.0 release is ready for early adopters interested in testing it out.
       You can use the development version, available on GitHub, by getting the
@@ -19,10 +15,10 @@ slug: announcements-4.0
         downloaded as a <code>zip</code> archive
       </a> as well.
     </p>
-  </section>
-
-  <hr />
+  </div>
+</section>
 
+<div class="container">
   <section id="release">
     <h1>Select2 4.0.0</h1>