code: function destroyDoc (docName, rev, callback) {
        if (!docName) {
          const msg = 'Invalid doc id'
          if (callback) {
            callback(msg, null)
          } else {
            return Promise.reject(msg)
          }
        } else {
          return relax({
            db: dbName,
            doc: docName,
            method: 'DELETE',
            qs: { rev: rev }
          }, callback)
        }
      }
docs: http://docs.couchdb.org/en/latest/api/document/common.html#delete--db-docid