fixed a typo in control.md

[adsick]

before

#![allow(unused)]
fn main() {
let bunny: SharedBunny = Rc::new(RefCell::(EnergizerBunny::new()));
}

after

#![allow(unused)]
fn main() {
let bunny: SharedBunny = Rc::new(RefCell::new(EnergizerBunny::new()));
}