gnucash-docs maint: Update copyright year of german guide

[Frank H.Ellenberger]

Updated	 via  https://github.com/Gnucash/gnucash-docs/commit/3a3ff9fe (commit)
	from  https://github.com/Gnucash/gnucash-docs/commit/3af01a65 (commit)



commit 3a3ff9fe1d0fa234461fcfe9c5ab13baf862761a
Author: Frank H. Ellenberger <frank.h.ellenberger at gmail.com>
Date:   Sat Jan 30 18:56:16 2021 +0100

    Update copyright year of german guide



Summary of changes:
 guide/de/gnucash-guide.xml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)