getNthSuffix (day) {
    switch (day) {
      case 1:
      case 21:
      case 31:
        return 'st'
      case 2:
      case 22:
        return 'nd'
      case 3:
      case 23:
        return 'rd'
      default:
        return 'th'
    }
  }
Get nth suffix for date
@param {Number} day
@return {String}