docs: Fix a few typos

[timgates42]

There are small typos in:

• bot.py
• core/irc.py
• plugins/dotnetpad.py
• plugins/down.py

Fixes:

• Should read language rather than langugage.
• Should read occurred rather than occured.
• Should read existence rather than existance.
• Should read connections rather than connetions.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md