code: function walkBack (startAt, lookingFor) {
    startAt = path.resolve(startAt)
    if (fs.existsSync(startAt) && fs.statSync(startAt).isDirectory()) {
      const dirs = path.resolve(startAt).split(path.sep)
      for (let i = 0; i < dirs.length; i++) {
        const basedir = i < dirs.length - 1
          ? dirs.slice(0, dirs.length - i).join(path.sep)
          : path.sep
  
        if (fs.existsSync(path.join(basedir, lookingFor))) {
          return path.join(basedir, lookingFor)
        }
      }
      /* if we reached here, nothing was found */
      return null
    } else {
      throw new Error('startAt path must be an existing directory: ' + startAt)
    }
  }
docs: Returns an absolute file path (if found) else `null`.
  
  @param {string} - the directory to start in
  @param {string} - the path we're looking for
  @return {string}
  @alias module:walk-back
  @example
  > walkBack('/Users/lloyd/Documents/75lb/walk-back', 'package.json')
  '/Users/lloyd/Documents/75lb/walk-back/package.json'
  
  > walkBack('/Users/lloyd/Documents/75lb/walk-back', '75lb')
  '/Users/lloyd/Documents/75lb'
  
  > walkBack('/Users/lloyd/Documents/75lb/walk-back', '.bash_profile')
  '/Users/lloyd/.bash_profile'
  
  > walkBack('.', '.bash_profile')
  '/Users/lloyd/.bash_profile'
  
  > walkBack('/Users/lloyd/Documents/75lb/walk-back', 'non-existent.file')
  null