Update the default recommended room version to v6
No changelog required - this is the index
MSC:
@@ -540,7 +540,7 @@ some other reason. Versions can switch between stable and unstable periodically
for a variety of reasons, including discovered security vulnerabilities and age.
Clients should not ask room administrators to upgrade their rooms if the room is
-running a stable version. Servers SHOULD use room version 5 as the default room
+running a stable version. Servers SHOULD use room version 6 as the default room
version when creating new rooms.
The available room versions are:
