Symbols are not rendering 
| -------------------------------------------------------------------------------------------------
| Reporting a bug or issue
| -------------------------------------------------------------------------------------------------

**Expected behavior:**

The react-sketchapp/examples/symbols project renders properly

**Observed behavior:**

It reports an error

```
/Users/calvinchan/react-sketchapp/examples/symbols  [git:master][calvinchan@ip-10-1-1-107] [15:03]
> yarn render
yarn run v1.6.0
$ skpm-build --watch --run
🖨  Copied src/manifest.json in 9ms
Error: Cannot render into Symbols page
line: 3109
sourceURL: /Users/calvinchan/react-sketchapp/examples/symbols/symbols.sketchplugin/Contents/Sketch/my-command.js
column: 16
stack: render@/Users/calvinchan/react-sketchapp/examples/symbols/symbols.sketchplugin/Contents/Sketch/my-command.js:3109:16
/Users/calvinchan/react-sketchapp/examples/symbols/symbols.sketchplugin/Contents/Sketch/my-command.js:4629:30
__skpm_run@/Users/calvinchan/react-sketchapp/examples/symbols/symbols.sketchplugin/Contents/Sketch/my-command.js:33077:17
__skpm_run@[native code]
🔩  Built ./my-command.js in 3249ms
```

**How to reproduce:**

clone repository and run `yarn render`

(on yarn 1.6)

**Sketch version:**

50.2

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