bot.sleep() can make memory leak

[sefirosweb]

• The FAQ doesn't contain a resolution to my issue

##Versions

• mineflayer: any

Detailed description of a problem

I found a bug on bot.sleep, if the bot cant execute sleep they can make a memory leak, the "event" is never closed:

mineflayer/lib/plugins/bed.js

Lines 161 to 164 in 195b3cb

	bot.once('sleep', () => {
	clearTimeout(timeoutForSleep)
	resolve()
	})

I saw my bot is increasing because the bot can't sleep

These are all events using my bot at real time, I saw never decrease "sleep" event until bot can sleep

I think they have a simply solution, i will made PR