Additionally, pin the irc library version to 18.0 because the newer
version has an error in the AioReactor:
```
File "/home/rht/code/venv/lib/python3.8/site-packages/irc/bot.py", line 108, in run
self.bot.reactor.scheduler.execute_after(intvl, self.check)
AttributeError: 'AioReactor' object has no attribute 'scheduler'
```