Use --depth=1 option when cloning

[trubitsyn]

This generally reduces traffic usage significantly by not cloning the whole repository but the most recent version. Though it seems like jgit has no support for this yet.

[Lonami]

Last time I looked for Git libraries, jgit was the only Java one I found that looked appealing :/

[Lonami]

https://stackoverflow.com/q/11475263/4759433 has more on this, for what is worth.