title: aiomultiprocess make a pool, but it doesn't work
body: <pre><code>import asyncio
  import aiohttp
  import time, json
  from aiomultiprocess import Pool
  
  start = time.time()
  url = 'http://member-service.test.cn/member/login'
  headers = {"Content-Type": "application/json;charset=UTF-8"}
  
  
  async def get(phone):
      session = aiohttp.ClientSession()
      response = await session.post(url=url, data=json.dumps(
          {"identityType": 1, "password": "111111", "platformSource": "Mall", "remember": True,
           "terminalType": "PC", 'identity': phone}), headers=headers)
      result = await response.text()
      session.close()
      print(result)
      return result
  
  
  async def request():
      phones = ['186%08d' % x for x in range(0, 10)]
      async with Pool() as pool:
          result = await pool.map(get, phones) # can't work
          return result
  
  coroutine = request()
  task = asyncio.ensure_future(coroutine)
  loop = asyncio.get_event_loop()
  loop.run_until_complete(task)
  
  end = time.time()
  print('Cost time:', end - start)
  </code></pre>
  
  <p>I try to use <code>aiomultiprocess</code> to make a pool. </p>
  
  <pre><code>async with Pool() as pool:
          result = await pool.map(get, phones) 
  </code></pre>
  
  <p>but actually can't call get function</p>