title: Exception event loop is closed with aiohttp and asyncio in python 3.8
body: <p>I am using asyncio and aiohttp to make concurrent requests. I've recently upgraded Python to version 3.8.0 and I'm getting a <code>RuntimeError: Event loop is closed</code> after the program has run.</p>
  
  <pre><code>import asyncio
  import aiohttp
  
  async def do_call(name, session):
      async with session.get('https://www.google.be') as response:
          await response.text()
          return 'ok - {}'.format(name)
  
  async def main():
      async with aiohttp.ClientSession() as session:
          tasks = [do_call(str(i), session) for i in range(0,4)]
          results = await asyncio.gather(*tasks)
          print(results)
  
  asyncio.run(main())
  </code></pre>
  
  <p>I do get a valid result from asyncio.gather(), but when exiting the exception is raised.
  I'd like to change the code so it doesn't run into exceptions.</p>
  
  <p>The traceback is as follows:</p>
  
  <pre><code>Exception ignored in: &lt;function _ProactorBasePipeTransport.__del__ at 0x000001E9A92079D0&gt;
  Traceback (most recent call last):
    File "C:\Users\Jonas\AppData\Local\Programs\Python\Python38\lib\asyncio\proactor_events.py", line 116, in __del__
      self.close()
    File "C:\Users\Jonas\AppData\Local\Programs\Python\Python38\lib\asyncio\proactor_events.py", line 108, in close
      self._loop.call_soon(self._call_connection_lost, None)
    File "C:\Users\Jonas\AppData\Local\Programs\Python\Python38\lib\asyncio\base_events.py", line 711, in call_soon
      self._check_closed()
    File "C:\Users\Jonas\AppData\Local\Programs\Python\Python38\lib\asyncio\base_events.py", line 504, in _check_closed
      raise RuntimeError('Event loop is closed')
  RuntimeError: Event loop is closed`
  </code></pre>