[PATCH] gitk: Update German translation

Attached to avoid whitespace problems. This patch is against master of 
gitk.git at git.kernel.org.

By the way, the following two keybinding explanations seem ambiguous to me:

  <Home>  Move to first commit
  <End>   Move to last commit

What happens is that <home> jumps to the newest commit and <end> jumps to the 
oldest commit. Whether the "first" commit should be the newest or the oldest 
is, well, somewhat ambiguous. I'd propose to talk about the newest or topmost 
commit, but rather not about the "first".

Regards,

Christian