build: fix days and dates in the %changelog of the spec-file

This prevents unneeded build warnings like:

    warning: bogus date in %changelog: Mon Apr 22 2008 ...

Bug: 1000019
Change-Id: Ie584e5faf5d04672186eada718aba7e71bd82b42
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/5692
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>