6.1.0

Fix return type in PHPDoc tags @nanato12 #322

Fix doc of getMember function.

isSucceeded return true if response code is 2xx @hinoguma #324

Change behavior of \LINEBot\Response#isSucceeded .Status code 200 ~ 299 -> true, other false.

Add keywords prop #325

Support this feature.
https://developers.line.biz/en/news/2020/12/02/messaging-api-update-december-2020/#keywords-news