MB-7250:  go back to using master branch for couchdbx-app, from plabee/MB-7250

Change-Id: I289b2b7175aa9c6b895e079a1e1d35e270674736
Reviewed-on: http://review.couchbase.org/41749
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>