aioredis now included in redis-py, please update imports

[sfarestam]

Note that aioredis is now included in redis-py (see https://github.com/aio-libs/aioredis-py), this means that this import in socketio/asyncio_redis_manager.py:

try:
    import aioredis
except ImportError:
    aioredis = None

can be updated to:

try:
    from redis import asyncio as aioredis
except ImportError:
    aioredis = None

or perhaps:

try:
    from redis import asyncio as aioredis
except ImportError:
    try:
        import aioredis
    except ImportError:
        aioredis = None