upgrade to pointycastle 4.0.0

I wonder if you could upgrade to pointycastle ^4.0.0 so I don't get the following error

```
Because encrypt 5.0.3 depends on pointycastle ^3.6.2 and no versions of encrypt match >5.0.3 <6.0.0, encrypt ^5.0.3
  requires pointycastle ^3.6.2.
So, because ment depends on both pointycastle ^4.0.0 and encrypt ^5.0.3, version solving failed.
```