fix doctests

src/osu/difficulty/gradual.rs

@@ -39,7 +39,7 @@ use super::{
 ///     .unchecked_into_converted::<Osu>();
 ///
 /// let difficulty = Difficulty::new().mods(64); // DT
-/// let mut iter = OsuGradualDifficulty::new(&difficulty, &converted);
+/// let mut iter = OsuGradualDifficulty::new(difficulty, &converted);
 ///
 ///  // the difficulty of the map after the first hit object
 /// let attrs1 = iter.next();

src/osu/performance/gradual.rs

@@ -28,7 +28,7 @@ use super::{OsuPerformanceAttributes, OsuScoreState};
 ///     .unchecked_into_converted::<Osu>();
 ///
 /// let difficulty = Difficulty::new().mods(64); // DT
-/// let mut gradual = OsuGradualPerformance::new(&difficulty, &converted);
+/// let mut gradual = OsuGradualPerformance::new(difficulty, &converted);
 /// let mut state = OsuScoreState::new(); // empty state, everything is on 0.
 ///
 /// // The first 10 hits are 300s and there are no sliders for additional combo