Change default room version from 9 to 10 (#1397)

* Change default room version from 9 to 10 in accordance with MSC3904

* Add changelog entry with assumed PR number.

* Fix missing comma in changelog.

Co-authored-by: Travis Ralston <travpc@gmail.com>

Co-authored-by: Travis Ralston <travpc@gmail.com>

changelogs/room_versions/newsfragments/1397.feature

@@ -0,0 +1 @@
+Update the default room version to 10, as per [MSC3904](https://github.com/matrix-org/matrix-spec-proposals/pull/3904).

content/rooms/_index.md

@@ -52,7 +52,7 @@ 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 9** as
+room is running a stable version. Servers SHOULD use **room version 10** as
 the default room version when creating new rooms.
 
 The available room versions are: