Update forms.ngdoc

docs(forms): Fixed a typo. render -> $render

Author: jbdeboer

docs/content/guide/forms.ngdoc

@@ -278,7 +278,7 @@ However, if you need more flexibility, you can write your own form control as a
 
 In order for custom control to work with `ngModel` and to achieve two-way data-binding it needs to:
 
-  - implement `render` method, which is responsible for rendering the data after it passed the {@link   api/ng.directive:ngModel.NgModelController#$formatters NgModelController#$formatters},
+  - implement `$render` method, which is responsible for rendering the data after it passed the {@link   api/ng.directive:ngModel.NgModelController#$formatters NgModelController#$formatters},
   - call `$setViewValue` method, whenever the user interacts with the control and model needs to be updated. This is usually done inside a DOM Event listener.
 
 See {@link guide/directive $compileProvider.directive} for more info.