doc: fix linter-enforced formatting in crypto.md

The markdown-linter (lint-md) is failing because of a missing newline
caused by 79d68150.

PR-URL: https://github.com/nodejs/node/pull/40780


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>