Fix a syntax error in leaking.md
@ -209,7 +209,7 @@ Usage looked like:
```rust,ignore
let mut data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
{
let guards = vec![];
let mut guards = vec![];
for x in &mut data {
// Move the mutable reference into the closure, and execute
// it on a different thread. The closure has a lifetime bound