Revert "custom scrollbar"

This reverts commit b962c16818b5b5a1d0df47286f8c013a50a4e097.
wtf
Merge branch 'gh-pages' of github.com:leela-test/tutorial into gh-pages

Conflicts:
	assets/toc.js
	assets/tutorial.css
	assets/tutorial.js
	assets/tutorial.styl