Remove bottom scrollbar

Currently the bottom scrollbar in the left-hand TOC is always present, even
when the content does not nearly reach the width of the TOC.

screenshot: https://skitch.com/kburke/en37s/dochub-instant-documentation-search

This adds one extra pixel of padding (from 14px to 15px), shrinking the box
width by 1px so that the scrollbar goes away.
Merge remote-tracking branch 'refs/remotes/kevinburke/scroll-in-toc' into lewang-master