rust immutable borrowing compiles when it shouldn't

Question

On the following Link, Where it mentions thinking in scopes, there's an example such as:

fn main() {
    let mut x = 5;
    let y = &mut x;

    *y += 1;

    println!("{}", x);
}

and it mentions that this will produce the error.

I run it on rust playground(https://play.rust-lang.org/) and seems like no error at all. Any idea why it's compiling ?