modify example of unfold so that it uses the initial_state value

Author: Erutuon

src/sources.rs

@@ -76,22 +76,21 @@ impl<A, F> Iterator for RepeatCall<F>
 ///
 /// use itertools::unfold;
 ///
-/// let (mut x1, mut x2) = (1u32, 1u32);
-/// let mut fibonacci = unfold((), move |_| {
+/// let mut fibonacci = unfold((1u32, 1u32), |(x1, x2)| {
 ///     // Attempt to get the next Fibonacci number
-///     let next = x1.saturating_add(x2);
+///     let next = x1.saturating_add(*x2);
 ///
 ///     // Shift left: ret <- x1 <- x2 <- next
-///     let ret = x1;
-///     x1 = x2;
-///     x2 = next;
+///     let ret = *x1;
+///     *x1 = *x2;
+///     *x2 = next;
 ///
 ///     // If addition has saturated at the maximum, we are finished
-///     if ret == x1 && ret > 1 {
-///         return None;
+///     if ret == *x1 && ret > 1 {
+///         None
+///     } else {
+///         Some(ret)
 ///     }
-///
-///     Some(ret)
 /// });
 ///
 /// itertools::assert_equal(fibonacci.by_ref().take(8),