add support for version 2 yaml files

[Davidsoff]

currently the tool only seems to support version 1 compose files. As this api version is getting deprecated it would be best for lorry to support version 2

https://docs.docker.com/compose/compose-file/#/version-2

[rupakg]

@Davidrums just wanted to update you that the original team was disbanded, so it it might be a while before any work is done here. Thanks for your interest in the project.