CouchDB Cradle `db.exists()` is broken and crashes entire application

Because of [this issue](https://github.com/flatiron/cradle/issues/289) sessionstore crashes [here](https://github.com/adrai/sessionstore/blob/f73c1eb136c00685571a6b15bdb5498f03590b12/lib/databases/couchdb.js#L137).
