chore: release spanner 1.27.0 (#4999)

Co-authored-by: Hengfeng Li <hengfeng@google.com>
diff --git a/spanner/CHANGES.md b/spanner/CHANGES.md
index 038cf7f..1da46d3 100644
--- a/spanner/CHANGES.md
+++ b/spanner/CHANGES.md
@@ -1,5 +1,12 @@
 # Changes
 
+## [1.27.0](https://www.github.com/googleapis/google-cloud-go/compare/spanner/v1.26.0...spanner/v1.27.0) (2021-10-19)
+
+
+### Features
+
+* **spanner:** implement valuer and scanner interfaces ([#4936](https://www.github.com/googleapis/google-cloud-go/issues/4936)) ([4537b45](https://www.github.com/googleapis/google-cloud-go/commit/4537b45d2611ce480abfb5d186b59e7258ec872c))
+
 ## [1.26.0](https://www.github.com/googleapis/google-cloud-go/compare/spanner/v1.25.0...spanner/v1.26.0) (2021-10-11)