[web-animations-1] Disambiguate interpolation definition source

Author: birtles

web-animations-1/Overview.bs

@@ -215,7 +215,7 @@ spec:dom; type:interface; text:Event
 spec:dom; type:dfn; for:/; text:shadow root
 spec:css-color-4; type:value; text:transparent
 spec:css-fonts-4; type:property; text:font-weight
-spec:css-values-3; type:type; text:<ident>
+spec:css-values-4; type:dfn; text:interpolation
 spec:css-backgrounds-3; type:property;
     text:border-width
     text:border-bottom-width