Incorrect url for @font-face rule

Hey,

one of the rule in _fonts.scss point to a non existent file in fonts directory, on the other hand there's no associated rule for the font Roboto-Thin.ttf. As I don't know what was your first idea (use Roboto-Thin or Roboto-Regular ?) I won't submit a PR.

Thanks for your works, it was very helpful for me.
