docs: function (db, directory, opts, cb) {
              if (isFunction(opts)) {
                  cb = opts;
                  opts = {};
              } else {
                  opts = opts || {};
              }
              opts = opts || {};
              return this.__getMigrator(directory).chain(function (Migrator) {
                  return new Migrator(db, directory, opts).run();
              }).classic(cb);
          }