Issue Description: Support for SkinsRestorer breaks with SR v14.1.0 because of a change in the net.skinsrestorer.bukkit.SkinsRestorer.getSkinsRestorerBukkitAPI() method.

• Dynmap Version: 3.2-beta1 (also happens with 3.1)
• Server Version: Paper 1.16.5 build #778
• Pastebin of Configuration.txt: https://gist.github.com/kdkasad/0e82ebae3a158be5efe4be9d6976db41
• Server Host (if applicable): N/A; self-hosted
• Pastebin of crashlogs or other relevant logs: https://gist.github.com/kdkasad/4167c83c489355e712029cc6081090bb

Steps to Replicate

1. Install SkinsRestorer v14.1.0
2. Set skinsrestorer-integration to true in Dynmap's configuration.
3. Start the server with Dynmap and SR installed

[ x ] I have looked at all other issues and this is not a duplicate
[ x ] I have been able to replicate this

More info

I don't know anything about how SkinsRestorer's API works or how to use it, but since I saw that the problem was a missing method, I tried to find out where that problem was introduced. It was in SkinsRestorer commit c454a09e28e2de94adc4986605eb36398a4dee04.

SkinsRestorer.skinsRestorerBukkitAPI was changed to SkinsRestorer.skinsRestorerAPI, which does not have a getter, and therefore cannot be accessed from Dynmap.

I'm sure that that is the problem, however I don't know the proper way to access the SkinsRestorer API since this change has been made.

I decided to take a look into how to access the SR API since I'd like to get this issue fixed as soon as possible.

From the example plugin provided by the SkinsRestorer devs, it looks like the correct way to fetch the SR API is using the net.skinsrestorer.api.SkinsRestorerAPI.getApi() static method.

I'll work on a fix and open a PR for it.