Improved Gloomhaven Boulder Storage

Small project to fix the one part of [Wolph42's](https://www.thingiverse.com/wolph42/about) excellent Gloomhaven storage set that was done imprecisely. While everything else in that group of prints fits snugly to the objects, the storage container for several items (bookcases, coffins, boulders, etc.) were done in wide boxes that take up extra space and cause the pieces to rattle around. This print fits them snugly.