doc: fix paragraph line-height issue

Fix a line-height issue introduced in #15660 where paragraphs
containing <code> blocks would have unequal line heights.

Fixes: https://github.com/nodejs/nodejs.org/issues/1399
PR-URL: https://github.com/nodejs/node/pull/16200


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>