Rename Widget::on_event to update

widget/src/button.rs

@@ -273,7 +273,7 @@ where
         });
     }
 
-    fn on_event(
+    fn update(
         &mut self,
         tree: &mut Tree,
         event: Event,
@@ -284,7 +284,7 @@ where
         shell: &mut Shell<'_, Message>,
         viewport: &Rectangle,
     ) {
-        self.content.as_widget_mut().on_event(
+        self.content.as_widget_mut().update(
             &mut tree.children[0],
             event.clone(),
             layout.children().next().unwrap(),