build: fix day in the %changelog

This fixes `warnings` during build tests `rpm.t`

Change-Id: I5609f1ab674ed0829e4d5ac049e4ca5d4f4b1a21
BUG: 1000019
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/6585
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>