Fix CSS bug with cookbook versions dropdown

:fork_and_knife: Adding overflow-y: scroll to foundations dropdown directly causes some strange CSS bugs and doesn't show the dropdown arrow. Instead this nests another unordered list within the dropdowns first list element and makes the nested unordered list scroll instead of the dropdown list.

 :arrow_down: Looks like this now.

![screen shot 2014-05-27 at 4 41 10 pm](https://cloud.githubusercontent.com/assets/316507/3097512/cb193ab8-e5df-11e3-9d05-81c4c4409632.png)