Support for --remove-orphans

[alexarana]

I would like to add support for the --remove-orphans option to this plugin.

The said option got added to version 1.7.0 of docker-compose back in April 2016. I have already done the change and am ready to prepare a PR if agreed.

@augi Thanks again for this very cool project.

[augi]

Hi, thanks!

If I understand the option correctly, it collects some garbage, so I'm for using this option by default.

According to changelog, this option can be used for up and down so I would prefer to use it for both commands by default.

Feel free to prepare the PR. It would be nice if the option would be specified only if docker-compose version >= 1.7.0 is detected.