[css-device-adapt] Silencing bikeshed warnings

Author: frivoal

css-device-adapt/Overview.bs

@@ -15,6 +15,7 @@ Former Editor: Ryan Betts, Adobe Systems, rbetts@adobe.com
 Former Editor: Øyvind Stenhaug, Opera Software, oyvinds@opera.com
 Abstract: This specification provides a way for an author to specify, in CSS, the size, zoom factor, and orientation of the viewport that is used as the base for the initial containing block.
 Issue Tracking: Bugzilla https://www.w3.org/Bugs/Public/buglist.cgi?component=Device%20Adaptation&list_id=52675&product=CSS&resolution=---
+Ignored Vars: <viewport-length>
 </pre>