DOC-2579: Update the example using mentions_fetch to reflect demo changes. (#3514)

* DOC-2579: Update the example using mentions_fetch to reflect demo changes.

* DOC-2579: correct syntax errors.

* Update modules/ROOT/partials/configuration/mentions_fetch.adoc

* Update modules/ROOT/partials/configuration/mentions_fetch.adoc

* DOC-2579: copy edits.

Author: kemister85

modules/ROOT/partials/configuration/mentions_fetch.adoc

@@ -26,9 +26,9 @@ tinymce.init({
       usersRequest = fetch('/users');
     }
     usersRequest.then((users) => {
-      // query.term is the text the user typed after the '@'
+      // `query.term` is the text the user typed after the '@'
       users = users.filter((user) => {
-        return user.name.indexOf(query.term.toLowerCase()) !== -1;
+        return user.name.toLowerCase().includes(query.term.toLowerCase());
       });
 
       users = users.slice(0, 10);