Issue Description: A minor bug. I don't know if it's just the configuration.txt spat out by the mod, or if it extends into the code, but I noticed "hide-if-invisiblity-potion" while editing the config for the first time...

• Dynmap Version: 3.1-beta6-forge-1.16.3
• Server Version: forge-1.16.5-36.0.13
• Pastebin of Configuration.txt: untouched, but here it is anyway
• Server Host (if applicable): self-hosted
• Pastebin of crashlogs or other relevant logs: N/A
• Other Relevant Data/Screenshots:
• Steps to Replicate: Right out of the box.

[:heavy_check_mark:] I have looked at all other issues and this is not a duplicate (as far as I can tell, mentions of hide-if-invisiblity-potion are due to quoted conffiles)
[:heavy_check_mark:] I have been able to replicate this

Because this would be a breaking change and the spelling error doesn't cause any errors and has existed this long we are going to leave it and not potentially break the 20k+ servers who use this plugin at any point in time. We have noted this down in the event we change our minds

A backwards-compatible solution would be to have the option available under both names, and use the misspelled version's value if the correctly spelled version is unset.

eg.

hideifinvisiblepotion = configuration.getBoolean(
   "hide-if-invisibility-potion",
   configuration.getBoolean("hide-if-invisiblity-potion", true)
);

I can confirm this is present in my copy of the configuration too.

The incorrect spelling appears to extend to the code:

"Misspelt".. couldn't resist