Remove shim

Isolate the scroll prevention

Specs shouldn't care about the shim
Solution to scrollbars not showing without a shim

Added a solution for the problem with overflow where scrollbars were not showing and added an explanation about this workaround as a commentary in .#nerdbox .nb-content.
Merge pull request #18 from Edearth/overflow

Solution to scrollbars not showing without a shim
Merge branch 'overflow'