fix grammar in rest-controllers.md (yiisoft#12087)

docs/guide/rest-controllers.md

@@ -82,7 +82,7 @@ than adding other filters described above, because the CORS filter has to be app
 and thus needs a slightly different approach compared to other filters. Also authentication has to be disabled for the
 [CORS Preflight requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS#Preflighted_requests)
 so that a browser can safely determine whether a request can be made beforehand without the need for sending
-authentication credentials. The follow code shows the code that is needed to add the [[yii\filters\Cors]] filter
+authentication credentials. The following shows the code that is needed to add the [[yii\filters\Cors]] filter
 to an existing controller that extends from [[yii\rest\ActiveController]]:
 
 ```php