everyone.

I am trying to create a simple telegram bot. In my country telegram is blocked so I need to work via proxy.

```
from telegram.ext import Updater         
from telegram.ext import CommandHandler  

import os

def start(bot, update):
    print("Hello")
    bot.sendMessage(chat_id=512562849, text="Hello.")

REQUEST_KWARGS={
    'proxy_url': 'http://93.171.217.48:10996',
    'urllib3_proxy_kwargs': {
    'username': '***',
    'password': '***',
    }
}

updater = Updater(token='<BOT_TOKEN>',
                  request_kwargs=REQUEST_KWARGS)  

start_handler = CommandHandler('start', start)  

updater.dispatcher.add_handler(start_handler)   
updater.start_polling()

```

But I have the next log

```
Exception in thread updater:
...
    _HTTPConnection.__init__(self, *args, **kw)
TypeError: __init__() got an unexpected keyword argument 'username'

```

I used [the next docs](https://github.com/python-telegram-bot/python-telegram-bot/wiki/Working-Behind-a-Proxy).

The free proxy works ok, but for my goals, it's bad to lose connection time after time. I prefer not to work under VPN either because of some bureaucracy in my company. 

Thanks in advance!