text: Title: DeprecationWarning: "@coroutine" decorator is deprecated since Python 3.8, use "async def" instead
  Body: I'm getting the exception below on Python 3.8:
  ```
  ...lib/python3.8/site-packages/aiofiles/os.py:10: DeprecationWarning: "@coroutine" decorator is deprecated since Python 3.8, use "async def" instead
      def run(*args, loop=None, executor=None, **kwargs):
  ```
  
  ```
  In [2]: aiofiles.__version__
  Out[2]: '0.5.0'
  ```