'svgLayers.layers' is undefined
**html-sketchapp version:** 4.0.0

Hi, I have came across an issue when using the story2sketch _(latest)_ package which has a dependency on html-sketchapp. 

When importing my asketch.json into Sketch I am coming across the following error:

_MOJavaScriptException: TypeError: svgLayer.layers is not a function. (In 'svgLayer.layers()', 'svgLayers.layers' is undefined)_

![image](https://user-images.githubusercontent.com/34164732/55082738-235d1800-509a-11e9-9097-529d75cd5fa7.png)

I have manged to pin point it to a single component in my repository which contains an SVG.

```
import React from 'react';

import icon from './chevron-down.svg';

/**
 * exampleComponent
 * @returns {void}
 */
const exampleComponent = () => (
    <div>
        <img src={icon} alt="chevron down" />
    </div>
);

export default exampleComponent;
```

chevron-down.svg:

`<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-chevron-down">
    <polyline points="6 9 12 15 18 9"></polyline>
</svg>`

If I give the SVG another child element for example:

`<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-chevron-down">
    <polyline points="6 9 12 15 18 9"></polyline>
    <polyline points="6 9 12 15 18 9"></polyline>
</svg>`

The issue is resolved and I no longer face an errors whilst importing the json file above.

Any help on this issue would be appreciated as I am unable to use the above as a solution to importing my components into sketch.
