Fix a typo in example code
Since the comment above the `reregister` call says "Even though the token
is the same", I'm guessing the author intended to pass the same Token as
the call to `register` above.
@@ -528,7 +528,7 @@ impl Registry {
/// // the token is the same it must be specified.
/// poll.registry().reregister(
/// &mut socket,
- /// Token(2),
+ /// Token(0),
/// Interest::WRITABLE)?;
/// # Ok(())
/// # }
