ReferenceError: Can't find variable: MSSharedStyleReference
Hi!

I'm developing a plugin to consolidate all symbols from different libraries into one.
To do this, I'm trying to use the libraries features for Sketch API, so I'm working on the branch  `feature/16238-add-support-for-libraries`.

I receive this error when I try to import the Sketch API. I'm working with the current Sketch version: 49.3.

``` javascript
import api from './api';

export default function(context) {
    console.log('RUN!', api.version);
    // var libraries = Library.getLibraries();
}
```

````
ReferenceError: Can't find variable: MSSharedStyleReference
line: 6274
sourceURL: /Users/iortega/repos/sketch-consolidate-library-symbols/plugin.sketchplugin/Contents/Sketch/consolidate-libraries.js
column: 74
````
