Allow universal selector with no namespace

Fixes #957.

Author: SelenIT

selectors/Overview.bs

@@ -3160,7 +3160,7 @@ Grammar</h2>
 	                    <<class-selector>> | <<attribute-selector>> |
 	                    <<pseudo-class-selector>> | <<pseudo-element-selector>>
 
-	<dfn>&lt;type-selector></dfn> = <<wq-name>> | <<ns-prefix>> '*'
+	<dfn>&lt;type-selector></dfn> = <<wq-name>> | <<ns-prefix>>? '*'
 
 	<dfn>&lt;ns-prefix></dfn> = [ <<ident-token>> | '*' ]? '|'