Fix typo in doc comment

lib/application.js

@@ -175,7 +175,7 @@ app.model = function(Model, config) {
  * ```
  *
  * 2. Use `app.model` to access a model by name.
- * `app.model` has properties for all defined models.
+ * `app.models` has properties for all defined models.
  *
  * The following example illustrates accessing the `Product` and `CustomerReceipt` models
  * using the `models` object.