Update changelog for 2.20.0 release

Author: acrobat

CHANGELOG.md

@@ -1,5 +1,16 @@
 # Changelog
 
+## 2.20.0
+
+### Added
+- Deployments: added missing 'delete deployment' endpoint ([clxmstaab](https://github.com/clxmstaab)) [#991](https://github.com/KnpLabs/php-github-api/issues/991)
+
+### Changed
+- phpdoc: fix typo ([clxmstaab](https://github.com/clxmstaab)) [#993](https://github.com/KnpLabs/php-github-api/issues/993)
+
+### Fixed
+- fixed php warning in GithubExceptionThrower ([clxmstaab](https://github.com/clxmstaab), [acrobat](https://github.com/acrobat)) [#992](https://github.com/KnpLabs/php-github-api/issues/992)
+
 ## 2.19.2
 
 ### Changed