Sass lint: use "stroustrup" as brace style convention

Sass lint: use "stroustrup" instead of "1TBS" as brace style convention.
See: https://en.wikipedia.org/wiki/Indent_style

Pros:
- Easily add or remove lines within a `@if`/`@else if`/`@else` block,
without having to rearrange the braces.
- Able to add comments that describe a condition (`@if (...)`, `@else
if (...)` or `@else`) or the whole conditional block.
- Clearly separate the different parts of the conditional block.

Cons:
- Not commonly used