doc: update changelog-maker instructions for releasing

The `changelog-maker` v5 removed the `--markdown` option, docs should
reflect that.

Signed-off-by: Juan José Arboleda <soyjuanarbol@gmail.com>
PR-URL: #65707
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Richard Lau <richard.lau@ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: juanarbol

doc/contributing/releases.md

@@ -447,15 +447,15 @@ Collect a formatted list of commits since the last release. Use
 [`changelog-maker`](https://github.com/nodejs/changelog-maker) to do this:
 
 ```bash
-changelog-maker --group --markdown
+changelog-maker --group --format=markdown
 ```
 
 `changelog-maker` counts commits since the last tag and if the last tag
 in the repository was not on the current branch you may have to supply a
 `--start-ref` argument:
 
 ```bash
-changelog-maker --group --markdown --filter-release --start-ref v1.2.2
+changelog-maker --group --format=markdown --filter-release --start-ref v1.2.2
 ```
 
 `--filter-release` will remove the release commit from the previous release.