Add serializer.jar to JARs bundled with reviki WAR.

serializer.jar is a dependency of xalan. Its absence from the WAR file
caused errors when generating the history page atom feed.

https://bugs.corefiling.com/show_bug.cgi?id=44456
Merge pull request #17 from paulcadman/bug44456

Fix for bug44456. HTTP 500 Error when viewing the atom feed of a history page