addDays = (startDate, days) => {
        const result = new Date(startDate);

        result.setDate(result.getDate() + days);

        return String(result);
    }
Calculates a new date by summing a given amount of days to a given date
@param  {String}  startDate      Date
@param  {Number}  days           Number of days to add
@return {String}                 Offsetted date