Update ApplicationCharge.php

This code is used to activate ApplicationCharge with $shopifySDK->ApplicationCharge($charge_id)->activate();

Author: salman0802

lib/ApplicationCharge.php

@@ -21,4 +21,9 @@ class ApplicationCharge extends ShopifyResource
      * @inheritDoc
      */
     public $countEnabled = false;
-}
+    
+    // To activate ApplicationCharge
+    protected $customPostActions = array(
+       'activate',
+   );
+}