Fixed Database_Tests.test18b_AttachmentMissingFile failure
Fixed Database_Tests.test18b_AttachmentMissingFile failure

Instead of accessing temp folder with /tmp, use NSTemporaryDirectory().

#1357

amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios