Fix typo in BoundPanel subclassing example

docs/releases/3.0.md

@@ -213,7 +213,7 @@ Binding to a request, instance and form object is now handled by a new class `Pa
 
 ```python
 class CustomPanel(Panel):
-    class BoundPanel(Panel.CustomPanel):
+    class BoundPanel(Panel.BoundPanel):
         def __init__(self, **kwargs):
             super().__init__(**kwargs)
             # The attributes self.panel, self.request, self.instance and self.form