Simple AJAX request

Hello. I'm try to emulate simple ajax request.

Scheme:

It' must return json:
`{phone: "8 xxx xxx-xx-xx"}`

But return `None` for me.
I'm suggest that the cause - cookies. Can someone help me with it?

```
# -*- coding: utf-8 -*-
import requests
import os, re, json, csv, sys
from robobrowser import RoboBrowser

class Aggregator(object):

def __init__(self, config):
main_url, output_file = [config.get(k) for k in sorted(config.keys())]
self.main_url = main_url
self.output_file = output_file

def start_process(self):

work_url = "https://m.avito.ru/sankt-peterburg/predlozheniya_uslug/almaznoe_burenie_almaznaya_rezka_usilenie_79225740"

session = requests.Session()
session.headers.update({
':host': 'm.avito.ru',
':method': 'GET',
':path': '/sankt-peterburg/predlozheniya_uslug/almaznoe_burenie_almaznaya_rezka_usilenie_79225740',
':scheme': 'https',
':version': 'HTTP/1.1',
'accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8',
'accept-encoding': 'gzip, deflate, sdch',
'accept-language': 'ru-RU,ru;q=0.8,en-US;q=0.6,en;q=0.4',
'cache-control': 'no-cache',
'pragma': 'no-cache',
'upgrade-insecure-requests': '1',
'user-agent': 'Mozilla/5.0 (X11; Linux i686) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2490.71 Safari/537.36',
'x-compress': 'null',
})
browser = RoboBrowser(session=session, history=True, parser='lxml')

browser.open(work_url)

phone_link = browser.find('a', {"class": "action-show-number"}).attrs['href'] + '?async'
browser.session.headers[':path'] = phone_link
browser.session.headers['accept'] = 'application/json, text/javascript, */*; q=0.01'
browser.session.headers['referer'] = work_url
browser.session.headers['upgrade-insecure-requests'] = ''
browser.session.headers['x-requested-with'] = 'XMLHttpRequest'
phone = browser.open(self.main_url + phone_link)

print(self.main_url + phone_link, phone)
print(browser.session.headers)
print(browser.session.cookies)

if __name__ == '__main__':
settings = { 'main_url': 'https://m.avito.ru', 'output_file': 'output.csv' }
aggregator = Aggregator(settings)
aggregator.start_process()
```

The issue provides a Python script using requests and RoboBrowser but names no repository file, test, or entry point. Start by reproducing the supplied request flow and inspect the returned value, session headers, and cookies. Done means determining whether RoboBrowser is responsible and documenting a reproducible fix or clear limitation.

Written by the indexing model from the issue text.