l10n: de.po: Reword generation numbers

The english term generation is here not used in the sense of "to
generate" but in the sense of "generations of beings".

This corrects the initial translation from cf4c0c2 (l10n: update German
translation, 2018-12-06).

Fixed-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>

Author: t-b

po/de.po

@@ -1535,7 +1535,7 @@ msgstr "Lösche Commit-Markierungen in Commit-Graph"
 
 #: commit-graph.c:1104
 msgid "Computing commit graph generation numbers"
-msgstr "Commit-Graph Generierungsnummern berechnen"
+msgstr "Commit-Graph Generationsnummern berechnen"
 
 #: commit-graph.c:1179
 #, c-format