The fab prefix is for FontAwesome Brand icons. The ranking-star icon is not a brand icon. It’s solid. So you don’t need any prefix.
That announcement is outdated. Discourse ships V7 since January. But there was no announcement 
The fab prefix is for FontAwesome Brand icons. The ranking-star icon is not a brand icon. It’s solid. So you don’t need any prefix.
That announcement is outdated. Discourse ships V7 since January. But there was no announcement