CBIT-532: Fix typo for {BUILD_NUMBER}

Change-Id: I735784fc490ceca5459deb93bfc78f35590d1e62
Reviewed-on: http://review.couchbase.org/37658
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Reviewed-by: Eric Limare <eric.limare@couchbase.com>
Tested-by: Eric Limare <eric.limare@couchbase.com>