This is just a suggestion to switch to a shallow git clone & fetch in the BuildTools using the `--depth=1` option.

Currently the `BuildTools` git clone & fetch operations download the complete git history of SpigotMC since ancient times. This commit history is very large (because of many commits). Git offers a solution to only get the latest state of the repository via `--depth`.

Contra:

• Replacement for `org.eclipse.jgit.api`.
    The currently used git library does not support the `--depth` option. 
• Maybe a little more implementation effort? E.g.: `Runtime.exec("git clone ...")`

Pro:

• `--depth=1`, means:
  • less traffic,
  • faster build times (local),
  • less costs for hosting hub.spigotmc.org
• A replacement for `jgit` could be the direct command call of `git`. One dependency less and a direct call of the dependent command. In my mind this is a win.

Why?
I'm building SpigotMC in a container without any fancy "caching" yet. So it does a "fresh" git clone and pull from the repo, which obviously creates a lot of traffic since it has to fetch the complete git history of SpigotMC.
I would like to reduce that pull-time & traffic, but `dont-update` doesn't work with `rev`.
Oh, and of course I'm hitting some kind of traffic firewall that nukes the speed of `git clone`.