Fix html error detected by test-suite

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

html.c

@@ -132,7 +132,7 @@ void html_option(char *value, char *text, char *selected_value)
 	html_attr(value);
 	html("'");
 	if (selected_value && !strcmp(selected_value, value))
-		html(" selected");
+		html(" selected='selected'");
 	html(">");
 	html_txt(text);
 	html("</option>\n");