This has been added recently in fd0a622. The problem is that the icon doesn't come from Fork Awesome but from Bootstrap. Because of this, it's got different dimensions, which makes it narrower than the other icons that come from Fork Awesome.

I can think of two possible fixes for this:

a) Tweak the CSS to make the icon's width identical to Fork Awesome icons. Maybe adding some padding/margin horizontally could fix this?

or

b) Replace the Bootstrap icon in this single instance with the signal icon from Fork Awesome, which uses the same dimensions as all the other currently used icons.