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 cf4c0c25 (l10n: update German
translation, 2018-12-06).

Fixed-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
diff --git a/po/de.po b/po/de.po
index 066326a..773e361 100644
--- a/po/de.po
+++ b/po/de.po
@@ -1535,7 +1535,7 @@
 
 #: 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