Added success/cancel boolean parameter to callback

I've seen multiple pull requests adding an extra parameter for the cancel. But like @pomartel suggest on pull #18 , just passing `true` on accept, `false`, on cancel should be enough and cleaner.

So it would be like 

```javascript
swal({
	title: "Are you sure?",
	text: "You will not be able to recover this imaginary file!",
	type: "warning",
	showCancelButton: true,
	confirmButtonColor: '#DD6B55',
	confirmButtonText: 'Yes, delete it!',
	closeOnConfirm: false
},
function(confirmed){
    if (confirmed){
        swal("Deleted!", "Your imaginary file has been deleted!", "success");
    } else {
        swal("Cancelled!", "Your imaginary file is safe!", "success");
    }
	
});
```