New Symfony 4 bin/composer directory structure (#9)

* New Symfony 4 bin/composer directory structure

Hi thanks for this helpful bundle. The update script anticipates the need to use 'bin' rather than 'app' but the method useNewDirectoryStructure is looking for symfony-var-dir option.  I added the symfony-bin-dir directory as an explicit option and the useNewDirectoryStructure method to look for that.  I think this will help keep the script working with projects independent of 'symfony-var-dir' .  Thanks!

* Update ScriptHandler.php

* Update ScriptHandler.php

* Update README.md

Took a deeper dive on this and it turns out we can just call the Command directly.  Updated the docs, thank you.

* Update README.md

README.md

@@ -138,6 +138,19 @@ Add to your `composer.json` event callbacks in a `scripts` section:
 }
 ```
 
+**Symfony >4 Flex**
+
+Add the command "geoip2:update": "symfony-cmd" to your autoscripts
+
+```json
+{
+    "scripts": {
+        "auto-scripts": {
+              "geoip2:update": "symfony-cmd"
+        },
+    }
+}
+```
 
 ## License
 

src/Composer/ScriptHandler.php

@@ -21,7 +21,7 @@ class ScriptHandler
      * to forthcoming listeners.
      */
     private static $options = [
-        'symfony-app-dir' => 'app',
+        'symfony-app-dir' => 'app' 
     ];
 
     /**
@@ -151,7 +151,7 @@ private static function hasDirectory(Event $event, $config_name, $path, $action_
      */
     private static function useNewDirectoryStructure(array $options)
     {
-        return isset($options['symfony-var-dir']) && is_dir($options['symfony-var-dir']);
+        return isset($options['symfony-bin-dir']) && is_dir($options['symfony-bin-dir']);
     }
 
     /**