Fix translation error of "complete => "vollständig" instead of
"unvollständig"
Currently: Documentation states that --unshallow can NOT be used on
INcomplete projects. This is wrong;
Correct would be: --unshallow can NOT be used on complete projects.
This change fixes that error in the German translation.
Signed-off-by: Philipp Weißmann <mail@philipp-weissmann.de> Reviewed-by: Matthias Rüster <matthias.ruester@gmail.com>