doc: fix name of the flag in initialize() docs

PR-URL: nodejs#49158
Reviewed-By: Debadree Chatterjee <debadree333@gmail.com>
Reviewed-By: Jacob Smith <jacob@frende.me>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

doc/api/esm.md

@@ -766,7 +766,7 @@ added: REPLACEME
 The `initialize` hook provides a way to define a custom function that runs
 in the loader's thread when the loader is initialized. Initialization happens
 when the loader is registered via [`register`][] or registered via the
-`--loader` command line option.
+`--experimental-loader` command line option.
 
 This hook can send and receive data from a [`register`][] invocation, including
 ports and other transferrable objects. The return value of `initialize` must be