fixed missing tokio feature

Cargo.toml

@@ -36,7 +36,7 @@ features = ["async-io", "std"]
 version = "1.2"
 optional = true
 default-features = false
-features = ["io-util"]
+features = ["fs", "io-util"]
 
 [dev-dependencies.tokio]
 version = "1.2"

src/taiko/pp.rs

@@ -62,7 +62,7 @@ impl<'map> TaikoPP<'map> {
         }
     }
 
-    /// Provide the result of previous a difficulty or performance calculation.
+    /// Provide the result of previous difficulty or performance calculation.
     /// If you already calculated the attributes for the current map-mod combination,
     /// be sure to put them in here so that they don't have to be recalculated.
     #[inline]