Added test for an issue found in the output of stats.includedFiles

Added test for issue
https://github.com/sass/node-sass/issues/522
True, `some()` is awesome! :+1: 

```javascript
['bar', 'foo'].map(function(expect) {
  var slug = fixture('include-files/' + expect + '.scss').replace(/\\/g, '/');

  assert(stats.includedFiles.some(function(s) {
    return s === slug;
  }));
});
```