Update @actions/exec to avoid passing the docker password on the command line

[domdfcoding]

Per the comment in DockerActionBuilder.ts:

push-prebuilt-action/src/DockerActionBuilder/DockerActionBuilder.ts

Lines 36 to 44 in 866e68e

	// Todo: use stdin
	// https://github.com/actions/toolkit/pull/360
	// waiting for new release.
	await exec.exec('docker login', [
	registry,
	'-u', user,
	'-p', token,
	])
	}

this depended on actions/toolkit#360, which has been merged. From what I can tell the changes made it into version 1.0.4

Would it be possible to have this updated to use stdin?

Thanks 😃