Layout--gutter-none results in wrong behaviour

[tqwewe]

Describe the bug
When attempting to create a layout with no gutter between the sidebar and main content, the resulting elements show a much larger gap.

The current Layout--gutter-none styles are:

&.Layout--gutter-none {
  --Layout-gutter: 0;
}

I believe the simple solution is to add a unit to the 0, such as 0px:

--Layout-gutter: 0px; /* with px suffix */

To Reproduce
Create a basic gutterless layout based on the docs here: https://primer.style/css/components/layout.

<div class="Layout Layout--gutter-none">
  <div class="Layout-main border">
    .Layout-main
  </div>

  <div class="Layout-sidebar border">
    .Layout-sidebar
  </div>
</div>

Expected behavior
There should be no gap between the sidebar and the main content.

Desktop (please complete the following information):

• OS: OSX
• Browser: Chrome
• Version: 19.2.0