Specifies `a` in link styling

That way, you can still have a class `.facebook` later on whose styling is unaffected by this. (Might not be a bad idea to just add a `.custom-link` class to accomplish a similar goal, and then use that in place of the `a` I just added)
Merge pull request #2 from j6k4m8/patch-2

Specifies `a` in link styling