Update isPostalCode.js

Taiwan has added in 2020 a 3+3 postal code format that is also available. 

https://www.post.gov.tw/post/internet/U_english2/index.jsp?ID=3509010116#:~:text=6%20digits.,serial%20number%E2%80%9D%20of%20ordinary%20households.

https://www.wikiwand.com/en/articles/Postal_codes_in_Taiwan

Even tho it's mainly for internal usage, it is still a valid format that might be required in some usecase. Therefore, I believe this library should consider it a valid postal code.

Author: Crocsx

src/lib/isPostalCode.js

@@ -69,7 +69,7 @@ const patterns = {
   SK: /^\d{3}\s?\d{2}$/,
   TH: fiveDigit,
   TN: fourDigit,
-  TW: /^\d{3}(\d{2})?$/,
+  TW: /^\d{3}(\d{2,3})?$/,
   UA: fiveDigit,
   US: /^\d{5}(-\d{4})?$/,
   ZA: fourDigit,