Added support for build key in v3
Added support for build key in v3

Resolves #636

This PR will add support for `build` in docker compose v3.
As https://github.com/docker/cli/pull/481 got merged now

kubernetes/kompose,skippbox/kompose,kadel/kompose,surajnarwade/kompose,procrypt/kompose,cdrage/kompose,cdrage/kompose,kadel/kompose,surajnarwade/kompose,skippbox/kompose,kubernetes/kompose,procrypt/kompose,procrypt/kompose,surajnarwade/kompose,skippbox/kompose