About record() function

Why record episode reward in this way? This makes the reward curve look nice but in fact it is not.
Why not just record the value of `ep_r`?

```
if global_ep_r.value == 0.:
      global_ep_r.value = ep_r
else:
      global_ep_r.value = global_ep_r.value * 0.99 + ep_r * 0.01
```