update the 2.1.20 changelog (#746)

Co-authored-by: arthur <[email protected]>

Author: ArthurKamalov

CHANGELOG.md

@@ -1,17 +1,19 @@
 Scalyr Agent 2 Changes By Release
 =================================
 
-## 2.1.20 "TBD" - TBD
+## 2.1.20 "Tabeisshi" - April 19, 2021
 
 <!---
-Packaged by Yan Shnayder <yan@scalyr.com> on Mar 9, 2021 14:00 -0800
+Packaged by Arthur Kamalov <arthur@scalyr.com> on April 19, 2021 21:00 -0800
 --->
 
 Improvements:
 * Add support for collecting some metrics Kubernetes when running in a CRI runtime.
 
 Bug fixes:
 * Ensure pod digest which we calculate and use to determine if pod info in the Kubernetes monitor has  changed is deterministic and doesn't depend on dictionary item ordering.
+* Fix a race condition in the worker session checkpoint read/write logic, which was introduced with the ``multi-worker`` feature.
+
 
 Other:
 * Changed the logging level of "not found" errors while querying pods from the Kubernetes API from ERROR to DEBUG, as these errors are always transient and result in no data loss.