SFTP plugin is very slow

Thanks for SFTP plugin to ScreenCloud
At the moment there is a problem with slow upload of screenshots to our SFTP server.

`[INFO] "Uploading screenshot to 'sftp'. Size: 8294400 bytes"`
Takes 3 minutes

If we use Monosnap or Joxy with upload to SFTP server - it takes few seconds.

It doesn't look like a network problem :)

Thank you!