Image URL not populating.
Example JSON

```
[
  {
    "hero":"http://www.mountain.org/sites/default/files/image_assets/5920447977_f84dff5a33_o_cropped_0.jpg"
    }
]
```

It seems that it's not populating,
<img width="1504" alt="screen shot 2016-06-02 at 11 22 28" src="https://cloud.githubusercontent.com/assets/6906867/15742156/2565f6a4-28b5-11e6-99b3-d1a4bea8ede2.png">

Any ideas? Sketch version is Version 3.8.3 (29802)
