made a little change for Amazon S3 API's compatibility
made a little change for Amazon S3 API's compatibility

k85169336/seaweedfs,hxiaodon/seaweedfs,chrislusf/seaweedfs,hxiaodon/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs,k85169336/seaweedfs