ws_connect doesn't follow proxy from environment

[lookis]

🐞 Describe the bug

I have set both http_proxy and https_proxy, with trust_env=True when create ClientSession,
everything is ok when get or post with this session, but for the ws_connect, It doesn't run with proxy.

💡 To Reproduce

background: I cann't visit wss://stream.binance.com:9443/ws under my network but it's ok with proxy

1. prepare a proxy at port 1086
2. http_proxy="http://127.0.0.1:1086"
3. https_proxy="https://127.0.0.1:1086"

import asyncio
import aiohttp
async def main():
    async with aiohttp.ClientSession(trust_env=True) as client:
        await client.ws_connect('wss://stream.binance.com:9443/ws')
        print('ok')

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

and it block forever (with a tcp handshake timeout exception)

💡 Expected behavior

just connect with proxy

📋 Logs/tracebacks

📋 Your version of the Python

$ python --version
Python 3.7.6

📋 Your version of the aiohttp/yarl/multidict distributions

$ python -m pip show aiohttp
Version: 3.6.2

$ python -m pip show multidict
Version: 4.7.5

$ python -m pip show yarl
Version: 1.1.0

📋 Additional context

aiohttp/aiohttp/client.py

Line 426 in bb7a4ea

if scheme == url.scheme:

scheme of websocket is ws or wss, url.scheme will always be http or https and ignore any other proxy here

aiohttp/aiohttp/helpers.py

Line 232 in bb7a4ea

if k in ('http', 'https')}

but it's ok for ws/wss to use http proxy

[webknjaz]

Feel free to send a PR with tests bundled.