Updating graph api version to 18.0 (#461)

Co-authored-by: Avinash Singhal <[email protected]>

Author: singhalavi

app/code/Meta/BusinessExtension/Helper/GraphAPIAdapter.php

@@ -53,7 +53,7 @@ class GraphAPIAdapter
     /**
      * @var string
      */
-    private $graphAPIVersion = '15.0';
+    private $graphAPIVersion = '18.0';
 
     /**
      * @var Client