chore(progressBar): fix api reference link

Author: marin-bratanov

controls/progressbar/server-side-programming.md

@@ -14,7 +14,7 @@ You can configure the settings of **RadProgressBar** and create its elements in
 
 ## RadProgressBar Public Properties and Methods
 
-For a list with the server-side properties and methods of the control, see the [Server-Side API of the RadProgressBar class](http://www.telerik.com/help/aspnet-ajax/t_telerik_web_ui_radprogressbar.html). You can also find it in the intellisense in Visual Studio.
+For a list with the server-side properties and methods of the control, see the [Server-Side API of the RadProgressBar class](https://testdocs.telerik.com/devtools/aspnet-ajax/api/server/Telerik.Web.UI/RadProgressBar). You can also find it in the intellisense in Visual Studio.
 
 ## Creating and Configuring a ProgressBar From the Code-behind