This looks like it's a typo on the docs page for the dribbble icon. In the code it's "dribble icon" with two b's, I tested in Chrome by changing it to 3 b's in the markup and it works.
However, I tried creating a fiddle and the dribbble icon works with 2 b's in it, but it does not work with 3 b's
So I'm not sure why the docs page would behave differently than when I'm using Semantic 2.2.1 on jsfiddle. Maybe the icon class names need to support both spellings ("dribble" and "dribbble")?
Fixes dribbble icon #4185