doc: fix s/rstStream/close in example

Backport-PR-URL: #20456
PR-URL: #18088
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

doc/api/http2.md

@@ -1015,7 +1015,7 @@ const { NGHTTP2_CANCEL } = http2.constants;
 const req = client.request({ ':path': '/' });
 
 // Cancel the stream if there's no activity after 5 seconds
-req.setTimeout(5000, () => req.rstStream(NGHTTP2_CANCEL));
+req.setTimeout(5000, () => req.close(NGHTTP2_CANCEL));
 ```
 
 #### http2stream.state