the creator property was removed in room v11, replace it with sender property

[ThomasHalwax]

https://spec.matrix.org/v1.9/rooms/v11/#remove-the-creator-property-of-mroomcreate-events

Update the code of roomstateReducer accordingly (https://github.com/syncpoint/matrix-client-api/blob/main/src/convenience.mjs#L51)