Change Korean Thanksgiving Day

[hweejae-shin]

Why Change

• South Korea observes a holiday for the day before and the day after Chuseok.
• However, the current data shows a three-day holiday from Chuseok itself.
• Therefore, the data should be modified to reflect a three-day holiday starting from the day before Chuseok.

Reference

• https://en.wikipedia.org/wiki/Chuseok

What Change

• Change Korean Thanksgiving Day data
• Update the unimplemented test code

[commenthol]

Hi @hweejae-shin,
Thanks for your PR. Can you please check why the tests are failing?
Please consider updating the fixtures with (See CONTRIBUTING.md):

npx mocha test/all.mocha.js --writetests --countries HK