Fix syntax error in notification ID assignment (#13)

Author: zonky2

docs/notification-center/developers/_index.en.md

@@ -26,7 +26,7 @@ class SomeService
 
     public function sendMessage(): void
     {
-        $notificationId = 42: // Usually, some module setting of yours where the user can select the desired notification
+        $notificationId = 42; // Usually, some module setting of yours where the user can select the desired notification
         $tokens = [
             'firstname' => 'value1',
             'lastname' => 'value2',   
@@ -273,4 +273,4 @@ sure this is shown e.g. in the `TokenContext::Email` context, this is your event
 
 This event is dispatched every time a `Parcel` was sent. It can be used to implement e.g. logging, retry logic etc.
 
-[DI_Autoconfigure]: https://symfony.com/doc/current/service_container.html#the-autoconfigure-option
+[DI_Autoconfigure]: https://symfony.com/doc/current/service_container.html#the-autoconfigure-option