Bump version to v7.1.5
Bump version to v7.1.5

Change-Id: I3cce2912735b99759544e35066d33627d0a2fc04
Reviewed-on: http://review.couchbase.org/99217
Reviewed-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>
Tested-by: Charles Dixon <e13bf4498b4994e133fd3586350658dc4a59329a@gmail.com>

brett19/gocbcore