Issue Description: Logging in navigates to /up/login and shows a JSON response instead of redirecting to index.html.
Same for registering.

• Dynmap Version: v3.1-beta4
• Server Version: Spigot 1.16.3
• Steps to Replicate: Enable login and register. After that also logging in reproduces this.

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

The problem is that login.html tries to load an older version of jQuery (1.11.0) instead the newer one (3.5.1). This results in 404 for the .js file and login.html:17 Uncaught ReferenceError: $ is not defined and eventually failing to redirect to /index.html.

Fixed in 9983bef

I can confirm that, too. Plugin version:

[18:37:04 INFO]: Dynmap version: core=3.1-beta4-421, plugin=3.1-beta4-421