Update example code to use `x/term` instead of `x/crypto/ssh/terminal`

Because x/crypto/ssh/terminal is deprecated and moved to x/term. https://pkg.go.dev/golang.org/x/crypto/ssh/terminal#pkg-overview

This will break compatibility with Go 1.13 though, is that right?

ssh/terminal is just the wrapper of x/term. https://github.com/golang/crypto/blob/master/ssh/terminal/terminal.go

So the code that was originally working keeps working and doesn't break compatibility with Go 1.13 I think(I could confirm that the updated example code working with Go 1.13).