doc: fix e.g., to e.g. in docs

PR-URL: https://github.com/nodejs/node/pull/18369
Fixes: https://github.com/nodejs/code-and-learn/issues/58


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>