MB-12274: Also point couchdbx-app to "2.5.1.1" branch

Change-Id: I0ed7cfee1103d107002d5d2076e75b37c94d48a7
Reviewed-on: http://review.couchbase.org/43353
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>