input: Write a python function to get the capital of a given country from the dictionary.
  assert get_capital('USA') == 'Washington DC'
  assert get_capital('Canada') == 'Ottawa'
  assert get_capital('Germany') == 'Berlin'
output: def get_capital(country):
      capitals = {
          'USA': 'Washington DC',
          'Canada': 'Ottawa',
          'Germany': 'Berlin'
      }
      return capitals.get(country, None)