doc: fix http2 example with rstWithCancel

Replace the non-existent method rstStreamWithCancel with rstWithCancel

PR-URL: nodejs/node#16365
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/http2.md

@@ -817,7 +817,7 @@ const client = http2.connect('http://example.org:8000');
 const req = client.request({ ':path': '/' });
 
 // Cancel the stream if there's no activity after 5 seconds
-req.setTimeout(5000, () => req.rstStreamWithCancel());
+req.setTimeout(5000, () => req.rstWithCancel());
 ```
 
 #### http2stream.state