doc: use italics for words-as-words

PR-URL: nodejs#22324
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Bryan English <bryan@bryanenglish.com>

doc/api/url.md

@@ -919,7 +919,7 @@ The legacy `urlObject` (`require('url').Url`) is created and returned by the
 #### urlObject.auth
 
 The `auth` property is the username and password portion of the URL, also
-referred to as "userinfo". This string subset follows the `protocol` and
+referred to as _userinfo_. This string subset follows the `protocol` and
 double slashes (if present) and precedes the `host` component, delimited by an
 ASCII "at sign" (`@`). The format of the string is `{username}[:{password}]`,
 with the `[:{password}]` portion being optional.