CHANGES.md: Add note about Go 1.6/1.8 support
## v0.32.0
+Note: This release is the last to support Go 1.6 and 1.8.
+
- bigquery:
- Add support for removing an expiration.
- Ignore NeverExpire in Table.Create.
- Align key checks.
- firestore:
- Return an error when using Start/End without providing values.
-- kms:
- - Add IAM methods.
- pubsub:
- Add pstest Close method.
- Clarify MaxExtension documentation.
- - Simplify ctx.Err check.
- securitycenter:
- Add v1beta1 client.
- spanner:
