Incorrect minification of `return [...iter].length` in babili 0.1.4

Minifying this in babili 0.1.4:

```js
function foo()
{
	return [...iter].length;
}
```

incorrectly outputs this:

```js
function foo() {
	return 1;
}
```

Babili can't tell at compile-time how many elements the iterator will return, so it's incorrect to assume it's always 1.