Improve headline.

Author: Florian Kissling

docs/announcements-4.0.html

@@ -5,7 +5,7 @@
 ---
 <section id="pre-release" class="jumbotron">
   <div class="container">
-    <h1>Pre-release notes</h1>
+    <h1>Announcing Select2 4.0.0</h1>
     <p class="lead">
       The 4.0 release is ready for early adopters interested in testing it out.
     </p>