doc: fix typo in http2.md

sendTrilers => sendTrailers.

PR-URL: https://github.com/nodejs/node/pull/26616


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>