Add PR 2131 to pending changelog.
Adds to pending changelog.
### SDK Enhancements
### SDK Bugs
+* `service/s3/s3manager`: Fix Download Manager with iterator docs ([#2131](https://github.com/aws/aws-sdk-go/pull/2131))
+ * Fixes the S3 Download manager's DownloadWithIterator documentation example.
+ * Fixes [#1824](https://github.com/aws/aws-sdk-go/issues/1824)
