Update CHANGELOG.md

Author: brizental

CHANGELOG.md

@@ -5,6 +5,7 @@
 * [#984](https://github.com/mozilla/glean.js/pull/984): BUGFIX: Return correct upload result in case an error happens while building a ping request.
 * [#988](https://github.com/mozilla/glean.js/pull/988): BUGFIX: Enforce rate limitation at upload time, not at ping submission time.
   * Note: This change required a big refactoring of the internal uploading logic.
+* [#1016](https://github.com/mozilla/glean.js/pull/1016): BUGFIX: Make shutdown a no-op in case Glean is not initialized.
 
 # v0.27.0 (2021-11-22)