### What it does
Checks for loops on `x.iter()` where `&x` will do, and
suggests the latter.

### Why is this bad?
Readability.

### Known problems
False negatives. We currently only warn on some known
types.

### Example
```
// with `y` a `Vec` or slice:
for x in y.iter() {
    // ..
}
```

Use instead:
```
for x in &y {
    // ..
}
```