[web-animations-1] Resolve DocumentOrShadowRoot link ambiguity

Author: birtles

web-animations-1/Overview.bs

@@ -190,6 +190,7 @@ urlPrefix: https://drafts.csswg.org/css-style-attr/; type: dfn; spec: css-style-
     text: style attribute
 </pre>
 <pre class="link-defaults">
+spec:dom; type:interface; text:DocumentOrShadowRoot
 spec:dom; type:interface; text:EventTarget
 spec:dom; type:interface; text:Event
 spec:dom; type:dfn; for:/; text:shadow root