[API] thumbnail_url is always empty

[mludowise]

Platform: API
API Version: v1

Steps to reproduce

Open http://api.sketchpacks.com/v1/plugins
Open https://api.sketchpacks.com/v1/plugins/com.mludowise.sketch-plugin-manager

Current behavior

The value for the thumbnail_url field is always empty string for every plugin.

Expected behavior

This field would point to the icon.png file located in the plugin's Resources folder if one exists. Sketch Plugin Manager has an icon.png file so I would expect it to be set in this field.

Workaround

None.