fix error

ps-grammar/object/object.jsgf

@@ -6,7 +6,7 @@ public <statement> = [<verb>] [<article>] <object> [please];
 <grab_object> = <cleaning_class> | <drink_class> | <snack_class> | <food_class> | tool | (bathroom stuff) | cleaning_stuff | drinks | snacks | object | food | something | stuff | item | beverage | things;
 <cleaning_class> = brush | detergent | shampoo | sponge | toothpaste;
 <drink_class> = (orange juice) | beer | cola | chocolate_milk | energy_drink | grape_juice | milk | water;
-<snack_class> = chocolate_cookies | chips | biscuits | bread | pringles | strawberry_cookies;
+<snack_class> = chocolate_cookies | chips | biscuits | bread | pringles | (strawberry cookies);
 <food_class> = baby_food | crackers | coffee | yeast | noodles | beans;