Render Failing

Command I am using
`terminalizer render demo`

Error I am getting
```
Error:
Error:
(electron:21848): Gtk-WARNING **: 15:15:48.011: Theme parsing error: gtk.css:6288:33: Junk at end of value for background-color

(electron:21848): Gtk-WARNING **: 15:15:48.011: Theme parsing error: gtk.css:6289:17: '' is not a valid color name

(electron:21848): Gtk-WARNING **: 15:15:48.011: Theme parsing error: gtk.css:6296:11: 'button' is not a valid property name

(electron:21848): Gtk-WARNING **: 15:15:48.011: Theme parsing error: gtk.css:6313:4: Expected semicolon

Hint:
Use the --help option to get help about the usage
```

I am using node 12.16.3 via npm
OS is Ubuntu 19.04

Start by reproducing `terminalizer render demo` with Node 12.16.3 on Ubuntu 19.04 and capture whether the GTK warnings accompany the render failure. Trace the render entry point from the CLI command, then verify that the command completes and produces the expected rendered output without the reported error.

Written by the indexing model from the issue text.