chore: added v0.20.x release notes (#182)

Author: devbww

CHANGELOG.md

@@ -1,6 +1,12 @@
 # Changelog
 
-## v0.20.x - TBD
+## v0.21.x - TBD
+
+## v0.20.x - 2020-02
+
+* feat: add new support for testing with environment variables (#180)
+* feat: logging can be enabled via env var (#181)
+* refactor: copy IsProtoEqual from spanner (#179)
 
 ## v0.19.x - 2020-02