Update dependencies

Among others, this updates minio-go, so that the new "eu-west-3" zone
for AWS is supported.

vendor/github.com/pkg/sftp/request-readme.md

@@ -11,7 +11,8 @@ manner.
 The Request structure has 5 public fields which you will deal with.
 
 - Method (string) - string name of incoming call
-- Filepath (string) - path of file to act on
+- Filepath (string) - POSIX path of file to act on
+- Flags (uint32) - 32bit bitmask value of file open/create flags
 - Attrs ([]byte) - byte string of file attribute data
 - Target (string) - target path for renames and sym-links
 
@@ -25,13 +26,18 @@ then sends to the client.
 ### Filewrite(*Request) (io.Writer, error)
 
 Handler for "Put" method and returns an io.Writer for the file which the server
-then writes the uploaded file to.
+then writes the uploaded file to. The file opening "pflags" are currently
+preserved in the Request.Flags field as a 32bit bitmask value. See the [SFTP
+spec](https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-6.3) for
+details.
 
 ###    Filecmd(*Request) error
 
 Handles "SetStat", "Rename", "Rmdir", "Mkdir"  and "Symlink" methods. Makes the
 appropriate changes and returns nil for success or an filesystem like error
-(eg. os.ErrNotExist).
+(eg. os.ErrNotExist). The attributes are currently propagated in their raw form
+([]byte) and will need to be unmarshalled to be useful. See the respond method
+on sshFxpSetstatPacket for example of you might want to do this.
 
 ### Fileinfo(*Request) ([]os.FileInfo, error)
 
@@ -44,5 +50,4 @@ Readlink).
 
 - Add support for API users to see trace/debugging info of what is going on
 inside SFTP server.
-- Consider adding support for SFTP file append only mode.
-
+- Unmarshal the file attributes into a structure on the Request object.