docs: Fix broken links in crypto.md

PR-URL: https://github.com/nodejs/node/pull/15182


Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>