Add PR 2129 to pending changelog
Adds PR to pending changelog.
### SDK Features
### SDK Enhancements
+* `private/model/api`: Add "Deprecated" to deprecated API operation and type doc strings ([#2129](https://github.com/aws/aws-sdk-go/pull/2129))
+ * Updates the SDK's code generation to include `Deprecated` in the documentation string for API operations and types that are depercated by a service.
+ * Related to [golang/go#10909](https://github.com/golang/go/issues/10909)
+ * https://blog.golang.org/godoc-documenting-go-code
### SDK Bugs
* `service/s3/s3manager`: Fix Download Manager with iterator docs ([#2131](https://github.com/aws/aws-sdk-go/pull/2131))
