update changelog

CHANGELOG.md

@@ -5,6 +5,7 @@
 * Fix `{#each}` context not shadowing outer scope when using `bind:` ([#1565](https://github.com/sveltejs/svelte/issues/1565))
 * Fix edge cases in matching selectors against elements ([#1710](https://github.com/sveltejs/svelte/issues/1710))
 * Allow exiting a reactive block early with `break $` ([#2828](https://github.com/sveltejs/svelte/issues/2828))
+* Don't lose `class:` directive classes on an element with `{...spread}` attributes when updating ([#3421](https://github.com/sveltejs/svelte/issues/3421))
 * Check attributes have changed before setting them to avoid image flicker ([#3579](https://github.com/sveltejs/svelte/pull/3579))
 * Fix generating malformed code for `{@debug}` tags with no dependencies ([#3588](https://github.com/sveltejs/svelte/issue/3588))
 * Fix generated code in specific case involving compound ifs and child components ([#3595](https://github.com/sveltejs/svelte/issue/3595))