Add missing fetch() in Model#where

Thanks to @tkrotoff for logging this, addresses #1240

src/model.js

@@ -1186,7 +1186,7 @@ const BookshelfModel = ModelBase.extend({
    * // or
    * model.where('favorite_color', 'red').fetch().then(function() { //...
    * // or
-   * model.where({favorite_color: 'red', shoe_size: 12}).then(function() { //...
+   * model.where({favorite_color: 'red', shoe_size: 12}).fetch().then(function() { //...
    *
    * @method Model#where
    * @param {Object|...string} method