Add a CHANGELOG.md entry

Author: Dexterp37

CHANGELOG.md

@@ -8,6 +8,7 @@
 * [#415](https://github.com/mozilla/glean.js/pull/415): Gzip ping paylod before upload
   * This changes the signature of `Uploader.post` to accept `string | Uint8Array` for the `body` parameter, instead of only `string`.
   * The gizpping functionality is disabled in Qt/QML environments. Follow [Bug 1716322](https://bugzilla.mozilla.org/show_bug.cgi?id=1716322) for updates on the status of this feature on that platform.
+* [#431](https://github.com/mozilla/glean.js/pull/431): BUGFIX: Record the timestamp for events before dispatching to the internal task queue.
 
 # v0.15.0 (2021-06-03)