[css2] Issue 196: remove 'hidden' from 'outline'

--HG--
extra : convert_revision : svn%3A73dc7c4b-06e6-40f3-b4f7-9ed1dbc14bfc/trunk%402558

Author: bert-github

css2/properties/properties.db

@@ -1014,7 +1014,7 @@ leftwards | rightwards | inherit;;
   no;;
   N/A;;
   visual, interactive;;
-  absolute length; '0' if the outline style is 'none' or 'hidden'
+  absolute length; '0' if the outline style is 'none'
 */