'bump version. Release 2.3.0'

Author: alek13

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Change Log
 
+## [2.3.0](https://github.com/php-slack/slack/releases/tag/2.3.0)
+ - Support PHP 8.1, 8.2, 8.3, 8.4
+   - Arguments with a null default must be nullable
+   - Test PHP 8.1 through 8.4
+   - Fix warnings for PHPUnit
+
 ## [2.2.1](https://github.com/php-slack/slack/releases/tag/2.2.1)
 - Update `.gitattributes`: Added /.styleci.yml export-ignore
 - Fix empty initial values in multi dynamic selects (fix #74)

README.md

@@ -10,7 +10,7 @@ A simple PHP package for sending messages to [Slack](https://slack.com)
 with [incoming webhooks](https://my.slack.com/services/new/incoming-webhook),
 focused on ease-of-use and elegant syntax.
 
-**supports:** PHP `7.1`, `7.2`, `7.3`, `7.4` or `8.0`  
+**supports:** PHP `7.1`, `7.2`, `7.3`, `7.4` or `8.0`, `8.1`, `8.2`, `8.3`, `8.4`  
 **require:** `guzzlehttp/guzzle` any of versions `~7.0|~6.0|~5.0|~4.0`
 
 > This is the fork of popular, great, but abandoned package [`maknz/slack`](https://github.com/maknz/slack)