Absolute image paths don't work
**Which version of the plugin are you using?**
[x] Data Populator for Sketch
[ ] Data Populator for Adobe XD

**Describe the bug**

Using absolute image paths appears not to work:

```
  {
    "title": "chrome.storage - Google Chrome",
    "icon": "/Volumes/Data/Work/Projects/Extensions/Tabnado/design/themes/icons/exist.png"
  },
```

The text populates, but the images don't.

Using relative image paths does work though.

**Expected behavior**
The images would be populated.

**Environment (please complete the following information):**
 - macOS Version: [macOS Sierra 10.12.6]
 - Sketch Version [Sketch 51.2]
 - Plugin Version [2.3.5 + 3.0.0]

**Additional context**
I tried also tried with with `file://` but that didn't work.
