Update change log

Author: yriveiro

CHANGELOG.md

@@ -2,6 +2,13 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## 2.1.0 - 2018-04-26
+### Changed
+- [#8](https://github.com/yriveiro/php-backoff/issues/8) Move phpstan to require-dev section
+- [#9](https://github.com/yriveiro/php-backoff/issues/9) Extract attempt validation to method
+- [#10](https://github.com/yriveiro/php-backoff/issues/10) Add type declarations to signature method where possible
+- [#11](https://github.com/yriveiro/php-backoff/issues/11) Method setOptions must honor the type of option param
+
 ## 2.0.2 - 2018-01-13
 ### Changed
 - Improve code fixing PHPStan complains.