gnucash-htdocs master: Correct the documentation links for 2.6.21 news.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash-htdocs/commit/63a79330 (commit)
	from  https://github.com/Gnucash/gnucash-htdocs/commit/05e679e6 (commit)



commit 63a7933099eb3f91c0d6e6e05c1917d3eb2f7ae7
Author: John Ralls <jralls at ceridwen.us>
Date:   Sun Jun 3 16:44:30 2018 -0700

    Correct the documentation links for 2.6.21 news.
    
    There is no doc release for 2.6.21, so make the links point to 2.6.20 docs.



Summary of changes:
 news/180410-2.6.21.news | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)