Fix ambiguous reference to 'allowed to use'

Author: lukewarlow

fullscreen.bs

@@ -11,6 +11,7 @@ Markup Shorthands: css no
 </pre>
 
 <pre class=link-defaults>
+spec:html; type:dfn; text:allowed to use
 spec:dom
     type:dfn; for:/; text:document
     type:dfn; for:/; text:element