Updating fb likebox dimensions to reflect new specs

The Facebook like box has new dimension specs. There is no longer a max
width, the default width is 300, the min width is 292.

Here are the new specs:
https://developers.facebook.com/docs/plugins/like-box-for-pages
Merge pull request #129 from bbrooks/fb-likebox-dimensions

Updating fb likebox dimensions to reflect new specs