fix: correct the Node.js script version extension in README.md.

README.md

@@ -28,9 +28,9 @@ You can override the look per request with the `look` query parameter, for examp
 or
 
 ```bash
-node ok-server.js
-node ok-server.js --look basic
-node ok-server.js --bind 127.0.0.1 --port 8080 --look bootstrap
+node ok-server.mjs
+node ok-server.mjs --look basic
+node ok-server.mjs --bind 127.0.0.1 --port 8080 --look bootstrap
 ```
 
 Connect to the server using a web browser or a tool like `curl`: