fixed typo

src/lib.rs

@@ -96,7 +96,7 @@
 //! let mods = 8 + 64; // HDDT
 //!
 //! // If you're only interested in the star rating or other difficulty value,
-//! // use `GradualDifficultyAttribtes`, either through its function `new`
+//! // use `GradualDifficultyAttributes`, either through its function `new`
 //! // or through the method `BeatmapExt::gradual_difficulty`.
 //! let gradual_difficulty = map.gradual_difficulty(mods);
 //!