input: Write a python function to get the quantity of a specific item from a fruit grocery class.
  assert FruitGrocery().get_item_quantity('Banana') == 200
  assert FruitGrocery().get_item_quantity('Orange') == 300
  assert FruitGrocery().get_item_quantity('Grapes') == 500
  assert FruitGrocery().get_item_quantity('Apple') == None
output: class FruitGrocery:
      def __init__(self):
          self.inventory = {
              'Banana': 200,
              'Orange': 300,
              'Grapes': 500
          }
      
      def get_item_quantity(self, item):
          return self.inventory.get(item)