Unable to login after last facebook update

Simply login code doesn't work
```
from fbchat import Client
client = Client("myemail@gmail.com", "mypassword")
```

## Traceback
```
Attempt #1 failed, retrying
Traceback (most recent call last):
File "C:\...\fbchat\_client.py", line 209, in login
user_agent=user_agent,
File "C:\...\fbchat\_state.py", line 149, in login
return cls.from_session(session=session)
File "C:\...\fbchat\_state.py", line 186, in from_session
fb_dtsg = FB_DTSG_REGEX.search(r.text).group(1)
AttributeError: 'NoneType' object has no attribute 'group'
```

## Environment information
- Python version 3.6
- `fbchat` version 1.9.6