Thread photo is tiny

## Description of the problem
The URL from fbchat.Client().fetchThreadInfo(t_id)[t_id].photo is really tiny, and I can't seem to find any way to change that URL to get a larger version.
fetchUserInfo() seems to do the same thing, so I can't even find a way to just get a different URL from the fbchat library.

## Code to reproduce
```py
# Example code
from fbchat import Client
client = Client("[REDACTED_USERNAME]", "[REDACTED_PASSWORD]")
(t,) = client.fetchThreadInfo("[REDACTED_THREAD_ID]")
print(t.photo)
## Open URL in browser, the photo is tiny
(t,) = client.fetchUserInfo("[REDACTED_User_ID]")
print(t.photo)
## As is this one
```

If I have to mess with the fbchat code to make this work better I'm happy to do some experimenting, but I get the feeling I'm missing something obvious because I can't seem to find any reference to anyone else struggling with this.