old_contents: class Cipher(object):
      def __init__(self):
          pass
  
  
  class Caesar(object):
      def __init__(self):
          pass
  
new_contents: class Cipher(object):
      def __init__(self, key=None):
          pass
  
      def encode(self, text):
          pass
  
      def decode(self, text):
          pass
  
  
  class Caesar(object):
      def __init__(self):
          pass
  
subject: Add parameters to exercise placeholder to resolve #640