Updated the code example of the documentation main page

doc/mainpage.hpp

@@ -46,7 +46,7 @@
 ///     {
 ///         // Process events
 ///         sf::Event event;
-///         while (window.GetEvent(event))
+///         while (window.PollEvent(event))
 ///         {
 ///             // Close window : exit
 ///             if (event.Type == sf::Event::Closed)