message: Fix missing lifetime in doc example for `Toggler`
diff: @@ -20,7 +20,7 @@ pub use iced_style::toggler::{Style, StyleSheet};
  /// # Example
  ///
  /// ```
  -/// # type Toggler<Message> = iced_native::widget::Toggler<Message, iced_native::renderer::Null>;
  +/// # type Toggler<'a, Message> = iced_native::widget::Toggler<'a, Message, iced_native::renderer::Null>;
  /// #
  /// pub enum Message {
  /// TogglerToggled(bool),
  