code: function checkPackageJsonInGit () {
    return exec('git', ['status', '--porcelain', 'package.json'])
      .then(function ([stdout, stderr]) {
        debug('git status --porcelain package.json', 'stdout', stdout, 'stderr', stderr)
        if (stdout.indexOf('package.json') >= 0) {
          throw new Error('package.json has changes!\n' +
            'I would like to add scripts to your package.json, but ' +
            'there are changes that have not been commited yet.\n' +
            'I don\'t want to damage anything, so I\'m not doing anyhting right now. ' +
            'Please commit your package.json')
        }
      })
  }
docs: Ensure that package.json is checked in and unmodified
  @return {Promise<boolean>} true, if everything is fine