#social-share-section anchor color always #fff

In beautifuljekyll.css the anchor color for #social-share-section is [unconditionally set to white](https://github.com/daattali/beautiful-jekyll/blob/master/assets/css/beautifuljekyll.css#L947). Added in c07c3ea3, it's not really obvious what its purpose is. For almost all of the social share links it doesn't matter as their color is white anyway, but for those that aren't (e.g. reddit), it overrides the correct color with white, due to specificity rules. I think it should just be removed altogether, unless there is a good reason for it?