skip parsing commits from dependency materials

I used the go-api-client and when I parsed this feed: https://go01.thoughtworks.com/go/api/pipelines/GreenInstallers/122316.xml it blew up parsing the commit because it was not a real commit, it was part of a dependency material. I don't know why Go represents them as changesets and maybe you want to model them in your domain specifically but for now I'm just skipping parsing them so I can use it.