fix(client-server): Fix a typo in /rooms/{roomId}/relations/{eventId}.

This patch fixes a typo in `/rooms/{roomId}/relations/{eventId}`. The
specification says about the `from` request query parameter:

> The pagination token to start returning results from. If not supplied,
> results start at the most recent topological event known to the
> server.
>
> Can be a `next_batch` or `prev_batch` token from a previous call,
> or a returned `start` token from `/messages`, or a `next_batch` token
> from `/sync`.

The last part is wrong. It should be:

> … or a `prev_batch` token from `/sync`.

Signed-off-by: Ivan Enderlin <ivan@mnt.io>

Author: Hywan

data/api/client-server/relations.yaml

@@ -254,7 +254,7 @@ components:
 
         Can be a `next_batch` or `prev_batch` token from a previous call, or a returned
         `start` token from [`/messages`](/client-server-api/#get_matrixclientv3roomsroomidmessages),
-        or a `next_batch` token from [`/sync`](/client-server-api/#get_matrixclientv3sync).
+        or a `prev_batch` token from [`/sync`](/client-server-api/#get_matrixclientv3sync).
       required: false
       example: page2_token
       schema: