docs(ngModel): fix example

For the example to work correctly, the initial model values have to be empty strings.

Closes #15272

Author: juboba

src/ng/directive/ngModel.js

@@ -469,7 +469,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
    *     angular.module('cancel-update-example', [])
    *
    *     .controller('CancelUpdateController', ['$scope', function($scope) {
-   *       $scope.model = {};
+   *       $scope.model = {value1: '', value2: ''};
    *
    *       $scope.setEmpty = function(e, value, rollback) {
    *         if (e.keyCode === 27) {
@@ -484,8 +484,8 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
    *   </file>
    *   <file name="index.html">
    *     <div ng-controller="CancelUpdateController">
-   *        <p>Both of these inputs are only updated if they are blurred. Hitting escape should
-   *        empty them. Follow these steps and observe the difference:</p>
+   *       <p>Both of these inputs are only updated if they are blurred. Hitting escape should
+   *       empty them. Follow these steps and observe the difference:</p>
    *       <ol>
    *         <li>Type something in the input. You will see that the model is not yet updated</li>
    *         <li>Press the Escape key.
@@ -502,17 +502,17 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
    *
    *       <form name="myForm" ng-model-options="{ updateOn: 'blur' }">
    *         <div>
-   *        <p id="inputDescription1">Without $rollbackViewValue():</p>
-   *         <input name="value1" aria-describedby="inputDescription1" ng-model="model.value1"
-   *                ng-keydown="setEmpty($event, 'value1')">
-   *         value1: "{{ model.value1 }}"
+   *           <p id="inputDescription1">Without $rollbackViewValue():</p>
+   *           <input name="value1" aria-describedby="inputDescription1" ng-model="model.value1"
+   *                  ng-keydown="setEmpty($event, 'value1')">
+   *           value1: "{{ model.value1 }}"
    *         </div>
    *
    *         <div>
-   *        <p id="inputDescription2">With $rollbackViewValue():</p>
-   *         <input name="value2" aria-describedby="inputDescription2" ng-model="model.value2"
-   *                ng-keydown="setEmpty($event, 'value2', true)">
-   *         value2: "{{ model.value2 }}"
+   *           <p id="inputDescription2">With $rollbackViewValue():</p>
+   *           <input name="value2" aria-describedby="inputDescription2" ng-model="model.value2"
+   *                  ng-keydown="setEmpty($event, 'value2', true)">
+   *           value2: "{{ model.value2 }}"
    *         </div>
    *       </form>
    *     </div>