Update persisted-model.js

`find` to `findById`

lib/persisted-model.js

@@ -158,7 +158,7 @@ module.exports = function(registry) {
    * @param {Object} instance Model instance matching the specified ID or null if no instance matches.
    */
 
-  PersistedModel.findById = function find(id, filter, cb) {
+  PersistedModel.findById = function findById(id, filter, cb) {
     throwNotAttached(this.modelName, 'findById');
   };