client.fetch_thread_info doesn't return correct group

## Description of the problem
Before updating to v2, I was able to use
```py
room = {"id": "room id here"}
group_info = client.fetchGroupInfo(room["id"])
participants = group_info[room["id"]].participants
client.set_items(room["id"], participants)
```
after I updated to v2 ( `2.0.0a5` ) I updated some code to:
```py
room = {"id": "room id here"}

# Error here
# client.fetch_thread_info(room["id"]) returns a wrong group thread.
# this is a generator so it not subscriptable to use client.fetch_thread_info(room["id"])[room["id"]]
group_info = client.fetch_thread_info(room["id"])
```
How can I get the group with the id that I passed?

## Code to reproduce
```py
group_info = client.fetch_thread_info(room["id"])
```

## Traceback
```
No traceback
```

## Environment information
- Python 3.7.4
- fbchat 2.0.0a5
- Windows 10