Upgrade to discord.js@12.0.0

[markokajzer]

What has been done

• Upgrade to discord.js v12
• Use @discordjs/opus to avoid deprecated and abandoned node-opus package
• Upgraded to Node v12
• Add .node-version file

How to test

• Confirm that every piece of functionality still works as expected
  • Check all commands
  • Check entrance / exit sounds
  • Check all config options

Notes

• See here for update guide
• Node v12 (newest) was not possible due to a transitive dependency of node-opus to a package called ref which is incompatible with Node v12
  • This is definitely a reason to ditch node-opus entirely in favor of opusscript
  • opusscript is said to be not very performant in the discord.js docs but how big is the difference? Is it really worth this whole hassle? I couldn't find any mentions of this outside of that README and it has been there since forever. Maybe the issues have been resolved?
  • Could also try ref-napi according to this comment

[markokajzer]

It seems like release of discord.js v12 is actually imminent after all this time if we look at their roadmaps and projects, so I'll put this on ice until the release sees the light of day.

[markokajzer]

cc @nstapelbroek LMAO 👌