Blank "space" with Missing Icon?

I have a blank space on http://paleo.io (at the bottom) that shouldn’t be there.

Basically, it’s a blank white bubble – looks like there’s supposed to be an icon there – but there isn’t.

I tried to fill out test urls on the icon sets before Facebook (dribble, etc), but that just adds a bubble in front of Facebook and moves this one farther to the left.

I’m having no other issues with this showing up any place else. Any idea on what it could be?

https://wordpress.org/plugins/simple-social-icons/