docs: Update changelog for version 1.6.3

git-svn-id: https://simplesamlphp.googlecode.com/svn/branches/simplesamlphp-1.6@2687 44740490-163a-0410-bde0-09ae8108e29a

docs/simplesamlphp-changelog.txt

@@ -6,6 +6,12 @@ simpleSAMLphp changelog
 This document lists the changes between versions of simpleSAMLphp.
 See the upgrade notes for specific information about upgrading.
 
+## Version 1.6.3
+
+Released 2010-12-16.
+
+  * Fix for cross site scripting in redirect page.
+
 ## Version 1.6.2
 
 Released 2010-07-29.