Bump to v2.1.1. Update changelog

Author: devblackops

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [2.1.1] - 2020-05-15
+
+### Fixed
+
+- Fixed reference to warning environment variable (`INPUT_FAILONWARNINGS`) (via [@CrazyCodeUK](https://github.com/CrazyCodeUK))
+
 ## [2.1.0] - 2020-05-15
 
 ### Changed