doc: use serial comma in tls.md

PR-URL: #17464
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

doc/api/tls.md

@@ -753,8 +753,8 @@ added: v0.8.4
 
 Verifies the certificate `cert` is issued to host `host`.
 
-Returns {Error} object, populating it with the reason, host and cert on failure.
-On success, returns {undefined}.
+Returns {Error} object, populating it with the reason, host, and cert on
+failure. On success, returns {undefined}.
 
 *Note*: This function can be overwritten by providing alternative function
 as part of the `options.checkServerIdentity` option passed to `tls.connect()`.