iPhone 6+ scale issue

The retina display from the iPhone 6+ has a scale of 3.

ofxQCAR.mm line 216 needs to be changed to:

```
  ARViewBoundsSize.width *= [UIScreen mainScreen].scale;
    ARViewBoundsSize.height *= [UIScreen mainScreen].scale;
```

Since the scale for non retina displays is 1 the if can be removed.
