Cannot login with 2FA when subject to Facebook checkup flow

## Description of the problem
Logging in fails when 2FA is enabled and Facebook requires a Facebook checkup flow.

## Code to reproduce
```py
from fbchat import Client
client = Client('', '')
```

## Traceback
```
Logging in ...
Please enter your 2FA code -->
Submitting 2FA code.
Saving browser.
Starting Facebook checkup flow.
Verifying login attempt.
Saving device again.
Attempt #1 failed, retrying
Please enter your 2FA code -->
```

## Environment information
- Python 3.7
- `fbchat` version 1.4.1