Intention: substitute associated type

[matklad]

Before:

impl Iterator for Foo {
    type Item = i32;

    fn next(&mut self) -> Option<<Self as /*caret*/ Iterator>::Item> {
        unimplemented!()
    }
}

After:

impl Iterator for Foo {
    type Item = i32;

    fn next(&mut self) -> Option</*caret*/i32> {
        unimplemented!()
    }
}