Fix s3manager Downloader copy paste comment errors
//
// The s3manager package's Downloader provides concurrently downloading of Objects
// from S3. The Downloader will write S3 Object content with an io.WriterAt.
-// Once the Downloader instance is created you can call Upload concurrently from
+// Once the Downloader instance is created you can call Download concurrently from
// multiple goroutines safely.
//
// // The session the S3 Downloader will use
// Key: aws.String(myString),
// })
// if err != nil {
-// return fmt.Errorf("failed to upload file, %v", err)
+// return fmt.Errorf("failed to download file, %v", err)
// }
// fmt.Printf("file downloaded, %d bytes\n", n)
//
