Update default SCSS configuration

`scss-lint` 0.31.0 made some [changes](https://github.com/causes/scss-lint/blob/master/CHANGELOG.md) to the default configuration.

This fixes the `style_guide/scss_spec`, but I'm still seeing 14 failures in unrelated specs:

```
ActionView::Template::Error:
  undefined method `bubbles?' for true:Sass::Script::Tree::Literal
```