code: function getCommits(repo, branchName) {
    return caller.call(repo, repo.commits, branchName)
    .then(function (commits) {
      return commits.map(function (commitObj) {
        return {
          id: commitObj.id,
          message: commitObj.message,
          committed_date: commitObj.committed_date
        }
      })
    })
  }
docs: /*
  List commits for specific branch