phpseclib v3 - ed25519 host key support

[rutek]

I think upgrade to phpseclib v3 is needed as v2 does not support ED25519 host keys. I noticed that new servers often generate ED25519 host key for SSH server so as for now it's impossible to use Flysystem SFTP adapter to connect to such servers.

[maxhelias]

You can use league/flysystem-sftp-v3