Update persisted-model.js

Note the PersistedMode.create() can take an array of instances, per #710.

lib/persisted-model.js

@@ -79,7 +79,7 @@ function convertNullToNotFoundError(ctx, cb) {
 /**
  * Create new instance of Model class, saved in database
  *
- * @param {Object} data Optional data object.
+ * @param {Object}|[{Object}] data Optional data object.  Can be either a single model instance or an array of instances.
  * @param {Function} cb Callback function with `cb(err, obj)` signature,
  *  where `err` is error object and `obj` is null or Model instance.
  */