corrected polarity of default timezone offset

[RyanWhipple]

The calculation of default timeZoneOffsets currently returns + when it should be - and vice-versa. This is because .getTimezoneOffset() returns a positive value for negative timezones and vice-versa.

Changing: const timeZoneOffset = getTimeZoneOffset(date.getTimezoneOffset() / 60); to: const timeZoneOffset = getTimeZoneOffset(-(date.getTimezoneOffset()) / 60); accounts for this reversal.

This corrects three scenarios:

---

• IF eventTime is not provided
• AND eventTimeZoneOffset is not provided
• THEN eventTime gets timeZone calculcated and appended with the wrong polarity

• AND eventTimeZoneOffset gets calculated with the wrong polarity

  objectEvent
  // .setEventTime("2022-09-28T10:11:49Z")
  // .setEventTimeZoneOffset("+08:00")
  
  // In my time zone (-07:00) yields:
  // "eventTimeZoneOffset": "+07:00",
  // "eventTime": "2022-10-10T15:14:11.154+07:00",

  ---

• IF eventTime is not provided
• AND eventTimeZoneOffset is provided

• THEN eventTime gets the timeZone calculated and appended with the wrong polarity

  objectEvent
  // .setEventTime("2022-09-28T10:11:49Z")
  .setEventTimeZoneOffset("+08:00")
  
  // In my time zone (-07:00) yields:
  // "eventTimeZoneOffset": "+08:00",
  // "eventTime": "2022-10-10T15:17:53.852+07:00",

  ---

• IF eventTime is provided with "Z" suffix
• AND eventTimeZoneOffset is not provided

• THEN eventTimeZoneOffset is calculated with the wrong polarity

  objectEvent
  .setEventTime("2022-09-28T10:11:49Z")
  // .setEventTimeZoneOffset("+08:00")
  
  // In my time zone (-07:00) yields:
  // "eventTimeZoneOffset": "+07:00",
  // "eventTime": "2022-09-28T10:11:49Z",