Sketch opens blank document
**Reporting a bug or issue**
running npm run render just opens a blank sketch document. 
Is there something else I need to be doing? I followed the steps in getting started to no avail. 

**Expected behavior:**
For a demo sketch file to open that's not blank. 

**Observed behavior:**
sketch file is blank.

**How to reproduce:**
npm run render

**Sketch version:**
43.2
