Update changelog for 2.16.0 release

Author: acrobat

CHANGELOG.md

@@ -1,5 +1,20 @@
 # Changelog
 
+## 2.16.0
+
+### Added
+- Add support for SSO errors coming from the API ([eiriksm](https://github.com/eiriksm)) [#913](https://github.com/KnpLabs/php-github-api/issues/913)
+- Add OutsideCollaborators api ([Matth--](https://github.com/Matth--)) [#925](https://github.com/KnpLabs/php-github-api/issues/925)
+- Add support for creating a repo dispatch event ([Nyholm](https://github.com/Nyholm)) [#931](https://github.com/KnpLabs/php-github-api/issues/931)
+
+### Changed
+- Fix: Wrong PHPDoc description ([OskarStark](https://github.com/OskarStark)) [#922](https://github.com/KnpLabs/php-github-api/issues/922)
+- Adding GitHub authentication to GraphQL documentation ([legionth](https://github.com/legionth)) [#927](https://github.com/KnpLabs/php-github-api/issues/927)
+
+### Fixed
+- Use RFC3986 for building URI query strings ([GrahamCampbell](https://github.com/GrahamCampbell)) [#908](https://github.com/KnpLabs/php-github-api/issues/908)
+- Fix call to test a webhook method ([morrislaptop](https://github.com/morrislaptop)) [#915](https://github.com/KnpLabs/php-github-api/issues/915)
+
 ## 2.15.0
 
 ### Added