doc: fix WHATWG URL url.protocol example

Protocol of `https://example.org` is `https:` not `http:`.

PR-URL: https://github.com/nodejs/node/pull/11647
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/url.md

@@ -599,7 +599,7 @@ Gets and sets the protocol portion of the URL.
 ```js
 const myURL = new URL('https://example.org');
 console.log(myURL.protocol);
-  // Prints http:
+  // Prints https:
 
 myURL.protocol = 'ftp';
 console.log(myURL.href);