Docker Login with --password-stdin

[MarZab]

Using --password is now a hard error, this requires STDIN to pass in the password.

[frankforpresident]

Documentation should be updated as it is not clear that you can provide stdin via the constructor. (same for env)

https://github.com/Quobject/docker-cli-js/blob/master/src/index.ts#L250

[frankforpresident]

I've created a PR for this. #31