gnucash maint: Release 2.6.21

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/9319858b (commit)
	from  https://github.com/Gnucash/gnucash/commit/655803a1 (commit)



commit 9319858b9697a8bf7ebad09be5235f8811baa64e
Author: John Ralls <jralls at ceridwen.us>
Date:   Mon Apr 9 15:30:36 2018 -0700

    Release 2.6.21



Summary of changes:
 CMakeLists.txt |  2 +-
 NEWS           | 10 ++++++++++
 configure.ac   |  2 +-
 3 files changed, 12 insertions(+), 2 deletions(-)