Updated Link from Pro Git to new book version

[iambastian]

This PR is a copy from #3152. I deleted my fork after pull so the update didn't integrate into my previous PR. @bluetata

What does this PR do?

For the german book "Pro Git" is a new version available. Updated the link for it.

For resources

Description

Why is this valuable (or not)

How do we know it's really free?

License notes are on the first page available.

For book lists, is it a book?

Checklist:

• Not a duplicate
• Included author(s) if appropriate
• Lists are in alphabetical order
• Needed indications added (PDF, access notes, under construction)

[bluetata]

LGTM~~awesome 👍

[eshellman]

Maybe it would be good to list both versions, since the v1 translation is smore complete than the v2 version; also maybe add a german "in-progress" annotation (see CONTRIBUTING.md)

[bluetata]

According to the CONTRIBUTING.md:

I suggest you can try to change it from

* [Pro Git 2009](http://git-scm.com/book/de/v1)
* [Pro Git - neue Version](http://git-scm.com/book/de/current) (:construction: *in process*)

to

* [Pro Git 1st Edition (2009)](http://git-scm.com/book/de/v1)
* [Pro Git 2nd Edition (2014)](http://git-scm.com/book/de/current) (:construction: *in process*)

<!-- or  -->

* [Pro Git (2009)](http://git-scm.com/book/de/v1)
* [Pro Git (neue Version)](http://git-scm.com/book/de/current) (:construction: *in process*)

<!-- or  -->

* [Pro Git (2009)](http://git-scm.com/book/de/v1)
* [Pro Git (2014)](http://git-scm.com/book/de/current) (:construction: *in process*)

[iambastian]

I took the 2nd suggestion, because the current-tag does not guarantee, that v2 will ever be the newest version. Thank you!

[eshellman]

Thanks, and welcome to free-programming-books!