Symbols not appearing
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| Reporting a bug or issue
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I was experimenting today with react-sketchapp and found that the symbol functionality does not work. Symbols don't appear on the generated Symbols page and do not show up when placed elsewhere in the document.

**Expected behavior:**
I can create and reuse symbols with react-sketchapp and have them appear on the generated Symbols page.

**Observed behavior:**
Symbols do not appear on either the generated Symbols page or as instances when I place them throughout the document with react-sketchapp.

**How to reproduce:**
Pull down the [symbols example project](https://github.com/airbnb/react-sketchapp/tree/master/examples/symbols) and run it.

**Sketch version:** 45.1

**Please attach screenshots, a zip file of your project, and/or a link to your github project**
