Update assignment 8

src/assignments/assignment08.rs

@@ -8,7 +8,7 @@
 /// Returns an anonymous function that applies the given function `f` for `n` times.
 ///
 /// For instance, `repeat(3, f)(x)` roughly translates to `f(f(f(x)))`.
-pub fn repeat<T, F: FnMut(T) -> T>(n: usize, f: F) -> impl FnMut(T) -> T {
+pub fn repeat<T, F: FnMut(T) -> T>(n: usize, mut f: F) -> impl FnMut(T) -> T {
     todo!();
     f // This line has been added to prevent compile error. You can erase this line.
 }