doc: fix linter-enforced formatting in crypto.md

The markdown-linter (lint-md) is failing because of a missing newline
caused by 79d681501d.

PR-URL: https://github.com/nodejs/node/pull/40780
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>

doc/api/crypto.md

@@ -2565,6 +2565,7 @@ added: v15.6.0
 The SHA-256 fingerprint of this certificate.
 
 ### `x509.fingerprint512`
+
 <!-- YAML
 added: REPLACEME
 -->