docs(ngModel.NgModelController): fix typo

Closes #14157

Author: cironunes

src/ng/directive/ngModel.js

@@ -292,7 +292,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
    *   the `$viewValue` are different from last time.
    *
    * Since `ng-model` does not do a deep watch, `$render()` is only invoked if the values of
-   * `$modelValue` and `$viewValue` are actually different from their previous value. If `$modelValue`
+   * `$modelValue` and `$viewValue` are actually different from their previous values. If `$modelValue`
    * or `$viewValue` are objects (rather than a string or number) then `$render()` will not be
    * invoked if you only change a property on the objects.
    */