Port CHANGELOG.md changes from v1.x to v2.x

Author: Art4

CHANGELOG.md

@@ -5,12 +5,19 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased](https://github.com/kbsali/php-redmine-api/compare/v1.8.0...master)
+## [Unreleased](https://github.com/kbsali/php-redmine-api/compare/v1.8.1...v2.x)
 
 ### Removed
 
 - **BREAKING**: Deprecated client `Redmine\Client` was removed, use `Redmine\Client\NativeCurlClient` or `Redmine\Client\Psr18Client` instead
 
+## [v1.8.1](https://github.com/kbsali/php-redmine-api/compare/v1.8.0...v1.8.1) - 2021-06-01
+
+### Fixed
+
+- `AbstractApi::get()` returns `null` on empty response body instead of `false` for BC reasons
+- Use uppercase in HTTP verbs
+
 ## [v1.8.0](https://github.com/kbsali/php-redmine-api/compare/v1.7.0...v1.8.0) - 2021-04-19
 
 ### Added