Rename v5 FontAwesome icons to match v6 name

While FontAwesome provides aliases for all icons, we switch to the new names for consistency. See all changes at:
https://fontawesome.com/docs/web/setup/upgrade/whats-changed#icons-renamed-in-version-6

app/assets/javascripts/exercises.js.erb

@@ -227,7 +227,7 @@ $(document).on('turbolinks:load', function () {
                 '<div class="list-group-item d-block" data-tip-id=' + tip.id + ' data-id="">' +
                 '<span class="fa fa-bars mr-3"></span>' + tip.title +
                 '<a class="fa fa-eye ml-2" href="/tips/' + tip.id + '" target="_blank"></a>' +
-                '<a class="fa fa-times ml-2 remove-tip" href="#""></a>' +
+                '<a class="fa fa-xmark ml-2 remove-tip" href="#""></a>' +
                 '<div class="list-group nested-sortable-list"></div>' +
                 '</div>';
             const tipList = $('#tip-list').append(template);