docs(ngHide): corrected logic in example

Closes #7436

src/ng/directive/ngShowHide.js

@@ -173,10 +173,10 @@ var ngShowDirective = ['$animate', function($animate) {
  *
  * ```html
  * <!-- when $scope.myValue is truthy (element is hidden) -->
- * <div ng-hide="myValue"></div>
+ * <div ng-hide="myValue" class="ng-hide"></div>
  *
  * <!-- when $scope.myValue is falsy (element is visible) -->
- * <div ng-hide="myValue" class="ng-hide"></div>
+ * <div ng-hide="myValue"></div>
  * ```
  *
  * When the ngHide expression evaluates to true then the .ng-hide CSS class is added to the class attribute