Update changelog

changelog.html

@@ -74,8 +74,10 @@ Upcoming changes</a>
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-20345">issue 20345</a>)
   <li class=bug>
     Broken CSS when reloading Jenkins after a time of inactivity
-    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-17526">issue 17526</a>)  
-  </li>
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-17526">issue 17526</a>)
+  <li class=bug>
+    Replace description in error dialog instead of appending
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-21457">issue 21457</a>)
 </ul>
 </div><!--=END=-->
 <h3><a name=v1.548>What's new in 1.548</a> (2014/01/20)</h3>