Change tense

Co-authored-by: Hubert Chathi <hubertc@matrix.org>

content/client-server-api/modules/voip_events.md

@@ -9,7 +9,7 @@ communication is supported (e.g. between two peers, or between a peer
 and a multi-point conferencing unit). This means that clients MUST only
 send call events to rooms with exactly two participants.
 
-All VoIP events have a `version` field. This will be used to determine whether
+All VoIP events have a `version` field. This is used to determine whether
 devices support this new version of the protocol. For example, clients can use
 this field to know whether to expect an `m.call.select_answer` event from their
 opponent. If clients see events with `version` other than `0` or `"1"`