chore(release): Prepare version 3.1.0

Author: pgrigoruta

CHANGELOG.md

@@ -3,12 +3,19 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
-## [Unreleased](https://github.com/contentful/contentful-management.php/compare/3.0.1...HEAD)
+## [Unreleased](https://github.com/contentful/contentful-management.php/compare/3.1.0...HEAD)
 
 <!-- PENDING-CHANGES -->
 > No meaningful changes since last release.
 <!-- /PENDING-CHANGES -->
 
+## [3.1.0](https://github.com/contentful/contentful-management.php/tree/3.1.0) (2020-03-24)
+
+### Added
+
+* stubs for new validators
+* allow genertaing richtext fields
+
 ## [3.0.1](https://github.com/contentful/contentful-management.php/tree/3.0.1) (2020-03-13)
 
 ### Changed