SCSS Compile Errors (replace / with math.div)

[plegner]

The latest version of Dart SCSS no longer supports / for division, to prevent conflicts with other CSS rules. For example,

$spacer-1: round($spacer / 2);

should be replaced with

@use "sass:map";
$spacer-1: round(math.div($spacer, 2));

Here are some instances where this happens:

css/support/variables/layout.scss 36:18
css/layout/grid.scss 4:18
css/layout/grid.scss 5:18
css/layout/grid.scss 6:18
css/layout/grid.scss 7:18

[mktcode]

Just trying out primer for the first time and I was like.... oh no... Please no warnings that I'll just have to accept for the time being. I'll try to prepare a PR. :D