Update migration_1_to_2.rst

docs/source/migration_1_to_2.rst

@@ -69,7 +69,7 @@ Also you can bind your own filters for using as keyword arguments:
         key = 'is_admin'
         
         def __init__(self, is_admin):
-            pass
+            self.is_admin = is_admin
             
         async def check(self, message: types.Message):
             member = await bot.get_chat_member(message.chat.id, message.from_user.id)