Variable cannot accessed from a closure function called from `setTimeout`.

Variable cannot accessed from a closure function called from `setTimeout`.

Related to #1 

```js
function abc() {
  var b = 20;
  
  return (function(){
    setTimeout(_ => console.log("b = " + b), 1000);
  })();
}

abc();
```

## Current result

```shell
b = undefined
```

## Expected result


```shell
b = 20
```
