Incorrect Send impl for Iter in chapter 7.8

[Icerath]

Iter<T> acts like a &T so it's Send impl should depend on T: Sync, not T: Send.

unsafe impl<'a, T: Send> Send for Iter<'a, T> {}

should be

unsafe impl<'a, T: Sync> Send for Iter<'a, T> {}

Here's some example code which shouldn't compile but does.

let mut list = LinkedList::new();
list.push_back(Cell::new(0));
let mut iter_a = list.iter();
let mut iter_b = list.iter();

std::thread::scope(move |scope| {
    scope.spawn(move || iter_a.next().unwrap().set(1));
    scope.spawn(move || iter_b.next().unwrap().set(2));
});