Add changelog for timestampsInSnapshots default change.
# Unreleased
+- [changed] The `timestampsInSnapshotsEnabled` setting is now enabled by
+ default so timestamp fields read from a `DocumentSnapshot` will be returned
+ as `Timestamp` objects instead of `Date`. Any code expecting to receive a
+ `Date` object must be updated.
# 17.1.5
- [changed] Firestore now recovers more quickly from bad network states.
