incorrect aliased/shadowed variable name when destructuring in the loop

input:

```js
function abc(items) {

if (items.length > 0) {
const params = 3;
console.log(params);
}

for (let [params, foo] of items) {
if (params) { // <--- here
console.log(foo);
}
}
}
```

output:

```js
function abc(items) {

if (items.length > 0) {
var params = 3;
console.log(params);
}

for (var i = 0, list = items; i < list.length; i += 1) {
var ref = list[i];
var params = ref[0];
var foo = ref[1];

if (params$1) { // <--- here
console.log(foo);
}
}
}
```
`params$1` is undeclared

It used to work in 0.18.0, but is broken in 0.19.0
Seems somewhat related to #94