Change the method of get server version.

[Dragonte6967]

As already announced before, at some point in the foreseeable future, we will remove the CraftBukkit package relocation (e.g. v1_20_R3). This may be as soon as 1.20.5, as we expect almost every plugin using internals to break due to major changes in vanilla anyways. https://forums.papermc.io/threads/important-dev-psa-future-removal-of-cb-package-relocation.1106/

Change the method of get server version. 1.20.5+ removed the CraftBukkit package relocation.