Run SAC Demo Error with one extra {}

```python
Traceback (most recent call last):
  File "/home/wangxs/d2rl/sac/main.py", line 71, in <module>
    group='{}_{}{}'.format(args.env_name, gym_env),
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
IndexError: Replacement index 2 out of range for positional args tuple
```

My Solution is  change the code 
```
group='{}_{}'.format(args.env_name, gym_env) 
```