gnucash-docs maint: Fix version number 2.6.21

[Frank H.Ellenberger]

Updated	 via  https://github.com/Gnucash/gnucash-docs/commit/ea2fe98a (commit)
	from  https://github.com/Gnucash/gnucash-docs/commit/4cfb9fe0 (commit)



commit ea2fe98aa7473a081f27fe96715c20af2593367c
Author: Frank H. Ellenberger <frank.h.ellenberger at gmail.com>
Date:   Tue Nov 12 06:32:32 2019 +0100

    Fix version number 2.6.21



Summary of changes:
 guide/C/appendixd.xml | 2 +-
 guide/C/ch_basics.xml | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)