updated UPDATE file

UPDATE.md

@@ -6,6 +6,11 @@ one. It only discusses changes that need to be done when using the "public"
 API of the framework. If you "hack" the core, you should probably follow the
 timeline closely anyway.
 
+beta4 to beta5
+--------------
+
+* `Response::isRedirected()` has been merged with `Response::isRedirect()`
+
 beta3 to beta4
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