Update CHANGELOG.md

Author: brizental

CHANGELOG.md

@@ -6,6 +6,7 @@
 * [#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.
 * [#1015](https://github.com/mozilla/glean.js/pull/1015): BUGFIX: Make attempting to call the `setUploadEnabled` API before initializing Glean a no-op.
+* [#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)