vendor: update github.com/goftp/server to fix hang while reading a file from the server

See: https://forum.rclone.org/t/minor-issue-with-linux-ftp-client-and-rclone-ftp-access-denied/8959

vendor/github.com/goftp/server/cmd.go

@@ -698,6 +698,9 @@ func (cmd commandRetr) Execute(conn *Conn, param string) {
 		defer data.Close()
 		conn.writeMessage(150, fmt.Sprintf("Data transfer starting %v bytes", bytes))
 		err = conn.sendOutofBandDataWriter(data)
+		if err != nil {
+			conn.writeMessage(551, "Error reading file")
+		}
 	} else {
 		conn.writeMessage(551, "File not available")
 	}

vendor/modules.txt

@@ -84,7 +84,7 @@ github.com/dropbox/dropbox-sdk-go-unofficial/dropbox/seen_state
 github.com/dropbox/dropbox-sdk-go-unofficial/dropbox/team_common
 github.com/dropbox/dropbox-sdk-go-unofficial/dropbox/team_policies
 github.com/dropbox/dropbox-sdk-go-unofficial/dropbox/users_common
-# github.com/goftp/server v0.0.0-20190111142836-88de73f463af
+# github.com/goftp/server v0.0.0-20190304020633-eabccc535b5a
 github.com/goftp/server
 # github.com/golang/protobuf v1.2.0
 github.com/golang/protobuf/proto