CBD-946:  still using "branch-20" of libconflate

Change-Id: I22d708d6d10df3d3216d538621ade4f600f19df0
Reviewed-on: http://review.couchbase.org/26766
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>