Fix set-cookie empty domain attribute parsing

We must not remove all domain attributes when we find an
empty domain attribute, we must only ignore this one particular
cookie-av. (RFC6265bis 5.3.3)

src/cow_cookie.erl

@@ -232,7 +232,7 @@ parse_set_cookie_attr(<<"max-age">>, Value) ->
 parse_set_cookie_attr(<<"domain">>, Value) ->
 	case Value of
 		<<>> ->
-			{ignore, domain};
+			ignore;
 		<<".",Rest/bits>> ->
 			{ok, domain, ?LOWER(Rest)};
 		_ ->