Updated CheckComboBox (markdown)

CheckComboBox.md

@@ -12,7 +12,7 @@ CheckComboBox is a combo box in which the items in the dropdown are preceded by
                              DisplayMemberPath="Color"
                              ValueMemberPath="Level"
                              SelectedValue="{Binding SelectedValue}"
-                             SelectedItems="{Binding SelectedItems}" />
+                             SelectedItemsOverride="{Binding SelectedItems}" />
 ```
 
 ### Properties