FIX: `coffee-mode` uses `coffee-tab-width` instead of `tab-width`.

And recently it has removed `tab-width` dependency completely.
Merge pull request #493 from pokehanai/hotfix/coffee-tabwidth

FIX: `coffee-mode` uses `coffee-tab-width` instead of `tab-width`.
Merge branch 'master' of git://github.com/bbatsov/prelude