test fix for a more stable condition (#3018)
test fix for a more stable condition (#3018)

* avoid the change listener is firing immedietly in case of faster device/machine. Making the purge happen after 0.5 wil be enough time to receive both change sets.
couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios