message: Fix `window::Renderer` link in `iced_winit` docs
diff: //! - A [`Widget`] trait, which is used to implement new widgets: from layout
  //! requirements to event and drawing logic.
  //! - A bunch of `Renderer` traits, meant to keep the crate renderer-agnostic.
  -//! - A [`window::Renderer`] trait, leveraging [`raw-window-handle`], which can be
  +//! - A [`window::Backend`] trait, leveraging [`raw-window-handle`], which can be
  //! implemented by graphical renderers that target _windows_. Window-based
  //! shells (like [`iced_winit`]) can use this trait to stay renderer-agnostic.
  //!
  //! [`druid`]: https://github.com/xi-editor/druid
  //! [`raw-window-handle`]: https://github.com/rust-windowing/raw-window-handle
  //! [`Widget`]: widget/trait.Widget.html
  -//! [`window::Renderer`]: window/trait.Renderer.html
  +//! [`window::Backend`]: window/trait.Backend.html
  //! [`UserInterface`]: struct.UserInterface.html
  //! [renderer]: renderer/index.html
  #![deny(missing_docs)]
  