v1.5.0 - Revamped update checker!

Changes:

• The update checker has been completely revamped!
• Previously, update checker contacted the SpigotMC API to check for updates,
  we now use the Modrinth API!

Why?

This change is being done to prepare for when I no longer post updates on Spigot.
While I love the Spigot platform, and will still support the server software for now,
its site is super outdated, writing change logs and posting updates has become tedious.

Along with that, this change allows me to give information about the update
when notifying users about the update!
This wasn't possible without switching API's (or at least wouldn't have been worth it)