Updated Link from Pro Git to new book version (#3153)

* Updated Link from Pro Git to new book version

* Update free-programming-books-de.md

* Update free-programming-books-de.md

free-programming-books-de.md

@@ -90,7 +90,8 @@
 
 * [Das Git-Buch](http://gitbu.ch) [PDF, EPUB]
 * [Git Magic](http://www-cs-students.stanford.edu/~blynn/gitmagic/intl/de/)
-* [Pro Git](http://git-scm.com/book/de/v1)
+* [Pro Git (2009)](http://git-scm.com/book/de/v1)
+* [Pro Git (neue Version)](http://git-scm.com/book/de/current) (:construction: *in process*)
 
 
 ### Groovy