code: function errorsText(errors, options) {
    errors = errors || this.errors;
    if (!errors) return 'No errors';
    options = options || {};
    var separator = options.separator === undefined ? ', ' : options.separator;
    var dataVar = options.dataVar === undefined ? 'data' : options.dataVar;
  
    var text = '';
    for (var i=0; i<errors.length; i++) {
      var e = errors[i];
      if (e) text += dataVar + e.dataPath + ' ' + e.message + separator;
    }
    return text.slice(0, -separator.length);
  }
docs: Convert array of error message objects to string
  @this   Ajv
  @param  {Array<Object>} errors optional array of validation errors, if not passed errors from the instance are used.
  @param  {Object} options optional options with properties `separator` and `dataVar`.
  @return {String} human readable string with all errors descriptions