s3: adding Location for multipart upload

fix https://github.com/chrislusf/seaweedfs/issues/1002

weed/s3api/filer_multipart.go

@@ -100,6 +100,7 @@ func (s3a *S3ApiServer) completeMultipartUpload(ctx context.Context, input *s3.C
 
 	output = &CompleteMultipartUploadResult{
 		CompleteMultipartUploadOutput: s3.CompleteMultipartUploadOutput{
+			Location: aws.String(fmt.Sprintf("http://%s%s/%s", s3a.option.Filer, dirName, entryName)),
 			Bucket: input.Bucket,
 			ETag:   aws.String("\"" + filer2.ETag(finalParts) + "\""),
 			Key:    objectKey(input.Key),