doc: fix heading type for v4.6.2 changelog

Originally was h2 should be h3

PR-URL: #9515
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

CHANGELOG.md

@@ -4,15 +4,15 @@
 
 This LTS release comes with 219 commits. This includes 80 commits that are docs related, 58 commits that are test related, 20 commits that are build / tool related, and 9 commits that are updates to dependencies.
 
-## Notable Changes
+### Notable Changes
 
 * **build**: It is now possible to build the documentation from the release tarball (Anna Henningsen) [#8413](https://github.com/nodejs/node/pull/8413)
 * **buffer**: Buffer.alloc() will no longer incorrectly return a zero filled buffer when an encoding is passed (Teddy Katz) [#9238](https://github.com/nodejs/node/pull/9238)
 * **deps**: upgrade npm in LTS to 2.15.11 (Kat Marchán) [#8928](https://github.com/nodejs/node/pull/8928)
 * **repl**: Enable tab completion for global properties (Lance Ball) [#7369](https://github.com/nodejs/node/pull/7369)
 * **url**: `url.format()` will now encode all `#` in `search` (Ilkka Myller) [#8072](https://github.com/nodejs/node/pull/8072)
 
-## Commits
+### Commits
 
 * [[`06a1c9bf80`](https://github.com/nodejs/node/commit/06a1c9bf80)] - **assert**: remove code that is never reached (Rich Trott) [#8132](https://github.com/nodejs/node/pull/8132)
 * [[`861e584d46`](https://github.com/nodejs/node/commit/861e584d46)] - **async_wrap**: add a missing case to test-async-wrap-throw-no-init (yorkie) [#8198](https://github.com/nodejs/node/pull/8198)