Replace jQuery.isFunction() checks with typeof

This method was deprecated in jQuery version 3.3, and removed from
jQuery as of version 4.0.0-beta.

  * https://api.jquery.com/category/deprecated/deprecated-3.3/
  * https://blog.jquery.com/2018/01/19/jquery-3-3-0-a-fragrant-bouquet-of-deprecations-and-is-that-a-new-feature/
  * https://blog.jquery.com/2024/02/06/jquery-4-0-0-beta/

Related to issue: #189

src/utility.js

@@ -135,12 +135,12 @@ function getTooltipContent(element) {
 		content;
 
 	if (tipText) {
-		if ($.isFunction(tipText)) {
+		if (typeof tipText === 'function') {
 			tipText = tipText.call(element[0]);
 		}
 		content = tipText;
 	} else if (tipObject) {
-		if ($.isFunction(tipObject)) {
+		if (typeof tipObject === 'function') {
 			tipObject = tipObject.call(element[0]);
 		}
 		if (tipObject.length > 0) {