message: Fix variable name in documentation
diff: @@ -191,7 +191,7 @@ pub fn get_time_since_start(ctx: &Context) -> time::Duration {
  /// This function will return true if the time since the
  /// last `update()` call has been equal to or greater to
  -/// the update FPS indicated by the `desired_update_rate`.
  +/// the update FPS indicated by the `target_fps`.
  /// It keeps track of fractional frames, so if you want
  /// 60 fps (16.67 ms/frame) and the game stutters so that
  /// there is 40 ms between `update()` calls, this will return
  